Transparent conductive thin film, process for producing the same, sintered target for producing the same, and transparent, electroconductive substrate for display panel, and organic electroluminiscence device

ABSTRACT

A transparent conductive thin film which can be produced easily by sputtering or the like with a sintered target, needs no post-treatment such as etching or grinding, is low in resistance and excellent in surface smoothness, and has a high transmittance in the low-wavelength region of visible rays; and transparent, electroconductive substrate for a display panel and an organic electroluminescence device excellent in light-emitting characteristics, both including the transparent conductive thin film. More particularly, a transparent conductive thin film comprising indium oxide as the major component and silicon as a dopant, having a substantially amorphous structure, wherein silicon is incorporated at 0.5 to 13% by atom on indium and silicon totaled; and a transparent conductive thin film comprising indium oxide as the major component and tungsten and germanium, wherein tungsten is incorporated at a W/In atomic ratio of 0.003 to 0.047 and germanium is incorporated at a Ge/In atomic ratio of 0.001 to 0.190.

This application is a divisional of prior application Ser. No.11/124,296 (filed on May 9, 2005, now U.S. Pat. No. 7,125,503) which isa divisional application of prior application Ser. No. 10/397,831 (filedon Mar. 27, 2003, now U.S. Pat. No. 6,911,163), the benefit of which isclaimed under 35 U.S.C. §120.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a transparent conductive thin film,process for producing the same, sintered target for producing the same,and transparent, electroconductive substrate for display panels andorganic electroluminescence devices, more particularly a transparentconductive thin film which can be produced easily by sputtering or thelike with a sintered target, needs no post-treatment such as etching orgrinding, is low in resistance and excellent in surface smoothness, andhas a high transmittance in the low-wavelength region of visible rays;and transparent, electroconductive substrate for display panel andorganic electroluminescence device excellent in light-emittingcharacteristics, both including the transparent conductive thin film.

2. Description of the Prior Art

A transparent conductive thin film has a high electroconductivity andhigh transmittance in the visible light region. Therefore, it has beenwidely used as a transparent electrode for various devices, e.g., solarcells, liquid-crystal displays (LCDs), display panels with anelectroluminescence device, and various types of light-receivingdevices.

It has been also used for heat ray reflecting films for windows ofautomobiles, buildings or the like, various types of antistatic films,and transparent heating devices for anti-fogging purposes for showcasescontaining frozen foods.

An electroluminescence device (hereinafter referred to as EL device) isa device that utilizes electroluminescence, and has been attracting muchattention as a light-emitting device for various types of displays,because of its high visibility and resistance to impact, the formercoming from its self-luminescence and the latter from being completelysolid. EL devices fall into two general categories of inorganic andorganic devices, the former using an inorganic compound as thelight-emitting material and the latter an organic compound. Organic ELdevices have been extensively studied for commercialization of displaysof the next generation, because they can be easily made compact bygreatly reducing the driving voltage. An organic EL device is composedof a laminate of anode/light-emitting layer/cathode as the basicstructure with a transparent conductive thin film as the anode formed ona transparent, electrically insulating substrate, e.g., glass sheet,where light is normally emitted from the substrate side.

Various materials have been extensively used for transparent conductivethin films. They include tin oxide (SnO₂) doped with antimony orfluorine, zinc oxide (ZnO) doped with aluminum or gallium, and indiumoxide (In₂O₃) doped with tin. In particular, films of indium oxide(In₂O₃) doped with tin, or In₂O₃—Sn-based films referred to as ITO(indium tin oxide) films, have been widely used because of easiness ofproducing low-resistance films.

The known processes for producing thin ITO films include spraying,vacuum evaporation, sputtering and ion plating. Sputtering is aneffective process for forming a film of a compound of low vapor pressureon an object (hereinafter merely referred to as substrate), or forming afilm whose thickness should be precisely controlled. It has been widelyused because it can be handled by a simple procedure. Ion plating is aprocess that ionizes the particles evaporated in a manner similar tothat for sputtering to improve their adhesive strength to the substrate,and then accelerates them in an electrical field onto the substrate, onwhich the film is securely formed.

Of these processes, sputtering is a film-making process which generatesan argon plasma by a glow discharge produced between the substrate asthe anode and a target as the cathode in an inert atmosphere (argon)kept at 0.1 to 10 Pa, and directs the resulting argon cations onto thetarget as the cathode to scatter the target component particles out ofthe cathode, which are deposited on the substrate.

This process is classified by method for producing the argon plasma;radio-frequency (RF) sputtering when radio-frequency (RF) plasma isused, and DC sputtering when DC plasma is used. The film can be producedby focusing argon plasma on immediately above the target by a magnetprovided on the backside of the target. This method is magnetronsputtering, which can have high argon ion collision efficiency even atlow gas pressure. DC magnetron sputtering is normally adopted to producetransparent conductive thin films of ITO.

Sintered ITO is normally used as the target. It is produced by a powdersintering process, in which indium oxide or tin oxide is incorporated tohave a substantially intended composition, pressed and sintered at 1400°C. or higher.

The target is normally of sintered ITO containing tin oxide (SnO₂) ataround 10% by weight, in particular the one having a density below 7.0g/cm³. More recently, sintered ITO of higher density and the targetusing such a sinter are being developed to improve film-makingcharacteristics of ITO.

A process for producing sintered ITO of high density (density: 7.02g/cm³ or more, or 98% or more as relative density) and high uniformity(scattering of around 1%) is disclosed by Japanese Patent Laid-openPublication No. 2000-144393. Sputtering with this ITO target gives goodfilms during the initial stage, but deteriorates in sputteringperformance (sputter rate) as the process time nears the final stage,because a black substance called nodule is generated on the targetsurface to cause problems, e.g., abnormal discharge. This phenomenonresults from uncontrolled pore distribution in the sinter. This meansthat its effects cannot be negligible, when sputtering lasts a longtime.

The electrode for LCDs and organic EL devices needs a transparentconductive thin film of surface smoothness and low resistance. Inparticular, an electrode for displays with an organic EL device needs atransparent conductive thin film of a highly smooth surface, because asuperthin film of organic compound is formed thereon. Surface smoothnessgenerally depends greatly on crystallinity of the film, and an amorphousfilm free of grain boundaries has a better surface smoothness than theothers of the same composition.

Even the ITO film of conventional composition is amorphous and has goodsurface smoothness, when formed by evaporation on a substrate kept at alow temperature (e.g., to 150° C. or lower) during the film-makingprocess. However, the film prepared by evaporation is insufficient indensity and adhesion to the substrate, and it is also insufficient infilm stability and repeatability. Therefore, it is not suitable for massproduction of transparent conductive thin films. On the other hand,sputtering is expected to give a film of excellent surface smoothness,when effected without heating the substrate during the film-makingprocess and at a high sputtering gas pressure (e.g., 2 Pa or more),because the film tends to be amorphous.

However, resistivity of the amorphous ITO film thus prepared is limitedto 6×10⁻⁴ to 8×10⁻⁴ Ω·cm. Therefore, it should have a sufficientthickness to form an electrode of low surface resistance to be usefulfor displays e.g., LCDs and organic EL devices. However, the ITO filmmay have a problem of coloration when its thickness exceeds 500 nm.

The ITO film, even when prepared by sputtering without heating thesubstrate, may be locally heated, because of high kinetic energy of thesputtered grains incident on the substrate, to form the mixed film ofthe amorphous phase contaminated with the fine crystalline phase. Thistendency is more noted as sputtering gas pressure decreases.

The fine crystalline phase present in the ITO film can be detected by atransmission electron microscope, in addition to X-ray diffractometer.It can deteriorate surface smoothness of the film, even when producedonly locally. Moreover, it may cause problems related to post-treatment,because it may selectively remain unremoved by etching with a weak acid,which is a necessary post-treatment step to remove fine projections onthe surface for surface smoothness.

Some processes for stably producing completely amorphous ITO films havebeen proposed. For example, Japanese Patent Laid-open Publication No.4-48516 discloses a process for producing an amorphous ITO film bysputtering the target while keeping the substrate at 100 to 120° C.,which is lower than crystallization temperature of ITO (around 150° C.).Japanese Patent Laid-open Publication No. 3-64450 discloses afilm-making process with hydrogen gas introduced into theoxygen-containing inert gas for sputtering.

However, the ITO film prepared at low temperature, although easilypatterned by wet etching because it is amorphous, involves problems ofincreased electrical resistivity and decreased visible raystransmittance. The process that includes photolithography for etchingthe amorphous ITO film formed on a substrate with hydrogen gasintroduced in the sputtering step and annealing for crystallization ofthe film cannot form the amorphous film at a sufficiently highfilm-making rate. The complicated process is another disadvantage.

Japanese Patent Laid-open Publication No. 62-202415 discloses a processfor producing an indium oxide film doped with silicon or silicon and tinby RF sputtering or electron beam evaporation. This process can producean indium oxide film doped with silicon or silicon and tin free of filmdefects, but the publication is silent on crystalline structure of thefilm, from which it is considered that it cannot give a film of surfacesmoothness even when it is prepared by RF sputtering in a pure argon gasatmosphere.

A Si-doped indium oxide film is totally crystalline, as observed byX-ray diffractometry, so it is not excepted to be an amorphous film thatis excellent in surface smoothness (refer to Appl. Phys. Let., vol. 64,1994, p. 1395).

An In₂O₃—ZnO-based film is known as a transparent, electroconductivefilm that is amorphous and excellent in surface smoothness, as disclosedby, e.g., Japanese Patent Laid-open Publication No. 6-234521. This filmcan keep its properties even when exposed to heat of 200° C., but it hasa lower transmittance than that of an ITO film in the low wavelengthregion of visible rays, because it contains metallic Zn. However, it mayhave the problem of unstable properties, because it is known thatmetallic Zn or ZnO present in the film tends to react with carbondioxide and moisture in air. Therefore, an In₂O₃—ZnO-based film isfunctionally insufficient for an LCD or organic EL device electrode.

Japanese Patent Laid-open Publication No. 11-323531 discloses atransparent conductive thin film of an amorphous In—Ge-based material.However, it has a high electrical resistivity of 8×10⁻⁴ Ω·cm or more,and is unsuitable for an LCD or organic EL device electrode.

More recently, an attempt has been made to use a transparent cathode foran EL device and to emit light from the cathode side. A light-receivingdevice transparent as a whole can be made when both anode and cathodeare made transparent. The transparent light-emitting device can performcolorful display while it is not emitting light, when an optional coloris used as a background color, to improve its decorativecharacteristics. For example, when black color is used as the backgroundcolor, the device can have improved contrast while it is emitting light.The EL device can be provided with a color filter or color conversionlayer as an accessory without considering the accessory while it isproduced, because the accessory can be placed on the light-emittingdevice. This provides the advantage of reducing electrode resistance,because it can be produced while increasing substrate temperature.

Under these situations, an attempt has been made recently to produce anorganic EL device with a transparent cathode. For example, JapanesePatent Laid-open Publication No. 10-162959 discloses an organic ELdevice having a structure with an electron-injecting metallic layercoming into contact with the organic layer by placing the organic layercontaining an organic light-emitting layer between the anode andcathode, the latter being composed of the electron-injecting metalliclayer and amorphous, transparent, electroconductive layer. JapanesePatent Laid-open Publication No. 2001-43980 discloses an organic ELdevice with a transparent cathode and light-reflecting metallic layer,e.g., that of Cr, Mo, W, Ta or Nb, for the anode so that it can emitlight more efficiently from the cathode.

However, each of these EL devices, containing an In₂O₃—ZnO-based film asthe transparent conductive thin film, has the problems of lowertransmittance than an ITO film in the low wavelength region of visiblerays, as discussed earlier, and unstable characteristics.

A transparent conductive thin film very high in surface smoothness, lowin resistance and high in transmittance is an essential part for variousdisplay panels, e.g., LCDs and organic EL devices, which are recentlybecoming increasingly more precise and fine. Therefore, there is a largedemand for easy processes capable of producing a transparent conductivethin film high in surface smoothness, low in resistance and high intransmittance.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a thin, transparent,electroconductive thin film which can be produced easily by sputteringor the like with a sintered target, needs no post-treatment such asetching or grinding, is low in resistance and excellent in surfacesmoothness, and has a high transmittance in the low-wavelength region ofvisible rays, in consideration of the above-described problems involvedin the conventional techniques. It is another object of the presentinvention to provide a process for producing the same. It is stillanother object of the present invention to provide a sintered target forproducing the same. It is still another object of the present inventionto provide a transparent, electroconductive substrate for display panelsand or organic electroluminescence devices, both including thetransparent conductive thin film.

Means for Solving the Problems

The inventors of the present invention have found, after havingextensively studied to solve the above problems by preparing transparentconductive thin films of varying composition by sputtering and examiningtheir crystalline structures, electric and optical characteristics indetail, that a transparent conductive thin film comprising indium oxideas the major component and silicon, indium oxide as the major componentand tungsten and silicon, or indium oxide as the major component andtungsten and germanium is useful for a transparent electrode film fororganic EL devices and LCDs, when prepared under specific conditions,because it is amorphous, and hence has excellent surface smoothness, andhas low electrical resistance and high transmittance of visible rays,achieving the present invention.

The first aspect of the present invention is a transparent conductivethin film comprising indium oxide as the major component and silicon,having a substantially amorphous structure, wherein silicon isincorporated at 0.5 to 13% by atom on indium and silicon totaled.

The second aspect of the present invention is the transparent conductivethin film of the first aspect, wherein at least one type of dopantselected from the group consisting of tin and tungsten is incorporated.

The third aspect of the present invention is the transparent conductivethin film of the second aspect, wherein tin is incorporated at 0.5 to15% by atom on tin and indium totaled.

The fourth aspect of the present invention is the transparent conductivethin film of the second aspect, wherein tungsten is incorporated at 0.2to 15% by atom on tungsten and indium totaled.

The fifth aspect of the present invention is the transparent conductivethin film of one of the first to fourth aspects that has a resistivityof 9.0×10⁻⁴ Ω·cm or less.

The sixth aspect of the present invention is the transparent conductivethin film of one of the first to fifth aspects that has an averagecenterline surface roughness (Ra) of 2.5 nm or less.

The seventh aspect of the present invention is the transparentconductive thin film of one of the first to sixth aspects which has anaverage transmittance of visible rays (400 to 800 nm) of 85% or more.

The eighth aspect of the present invention is the transparent conductivethin film of one of the first to seventh aspects which has acrystallization temperature of 180° C. or higher.

The ninth aspect of the present invention is a transparent conductivethin film comprising indium oxide as the major component and tungstenand germanium, wherein tungsten is incorporated at a W/In atomic ratioof 0.003 to 0.047 and germanium is incorporated at a Ge/In atomic ratioof 0.001 to 0.190.

The tenth aspect of the present invention is the transparent conductivethin film of the ninth aspect, wherein tungsten is incorporated at aW/In atomic ratio of 0.005 to 0.026 and germanium is incorporated at aGe/In atomic ratio of 0.033 to 0.190.

The 11^(th) aspect of the present invention is the transparentconductive thin film of ninth aspect that has a resistivity of 8.0×10⁻⁴Ω·cm or less.

The 12^(th) aspect of the present invention is the transparentconductive thin film of the 11^(th) aspect that has a resistivity of4.0×10⁻⁴ Ω·cm or less.

The 13^(th) aspect of the present invention is the transparentconductive thin film of ninth aspect, wherein the thin film structure issubstantially amorphous, as determined by X-ray diffractometry.

The 14^(th) aspect of the present invention is the transparentconductive thin film of ninth aspect which has a crystallizationtemperature of 180° C. or higher.

The 15^(th) aspect of the present invention is the transparentconductive thin film of ninth aspect that has a surface roughness (Ra)of 1.5 nm or less.

The 16^(th) aspect of the present invention is a sintered target forproducing the transparent conductive thin film of one of the first toeighth aspects, wherein a plurality of silicon chips are put up, atalmost the same intervals, on a sintered target selected from the groupconsisting of sintered indium oxide, indium oxide doped with tin andindium oxide doped with tungsten.

The 17^(th) aspect of the present invention is a sintered target forproducing the transparent conductive thin film of one of the first toeighth aspects, wherein the sintered target is selected from the groupconsisting of sintered indium oxide doped with silicon, and indium oxidedoped with silicon together with tin and/or tungsten.

The 18^(th) aspect of the present invention is a sintered target forproducing the transparent conductive thin film of one of the ninth to15^(th) aspects, comprising indium oxide as the major component andtungsten and germanium, wherein tungsten is incorporated at a W/Inatomic ratio of 0.003 to 0.045 and germanium is incorporated at a Ge/Inatomic ratio of 0.001 to 0.256.

The 19^(th) aspect of the present invention is the sintered target ofthe 18^(th) aspect that is used as a target for sputtering or ionplating.

The 20^(th) aspect of the present invention is the sintered target ofthe 18^(th) aspect that has a surface roughness (Rmax) of 2.9 μm or lesson the sputtered surface.

The 21^(st) aspect of the present invention is a process for producing athin, amorphous, transparent, electroconductive film comprisingsilicon-doped indium oxide on a substrate by sputtering in anoxygen-containing inert gas atmosphere in a sputtering apparatus thatcontains the substrate and sintered target of the 16^(th) or 17^(th)aspect.

The 22^(nd) aspect of the present invention is the process of the21^(st) aspect for producing a transparent conductive thin film, whereinthe substrate is heated at 100 to 300° C.

The 23^(rd) aspect of the present invention is the process of the21^(st) aspect for producing a transparent conductive thin film, whereinthe inert gas is a mixture of argon gas and oxygen containing oxygen at1% or more.

The 24^(th) aspect of the present invention is the process of the21^(st) aspect for producing a transparent conductive thin film, whereinthe film is produced by DC sputtering in an oxygen-containing inert gasatmosphere after pressure in the sputtering apparatus is set at 0.1 to 1Pa.

The 25^(th) aspect of the present invention is a process for producing atransparent conductive thin film comprising indium oxide doped withtungsten and germanium on a substrate by sputtering or ion plating withthe sintered target of the 18^(th) aspect.

The 26^(th) aspect of the present invention is a transparent,electroconductive substrate for display panels, comprising thetransparent conductive thin film of one of the first to 15^(th) aspectsformed on a substrate selected from the group consisting of glasssubstrate, quartz plate and resin plate or film.

The 27^(th) aspect of the present invention is the transparent,electroconductive substrate of the 26^(th) aspect for display panels,wherein the substrate is coated with at least one layer selected fromthe group consisting of electrically insulating, semi-conductor, gasbarrier and protective layers.

The 28^(th) aspect of the present invention is an organicelectroluminescence device which uses the transparent conductive thinfilm of one of the first to 15^(th) aspects as the anode and/or cathode.

The 29^(th) aspect of the present invention is the organicelectroluminescence device of the 28^(th) aspect, wherein the anodecomprises a thin, light-reflecting film and the cathode comprises atransparent conductive thin film or transparent conductive thin film andmetallic thin film.

The 30^(th) aspect of the present invention is an organicelectroluminescence device which comprises an organic layer and cathodeformed on an anode of the transparent, electroconductive substrateaccording to Claim 26 for display panels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an X-ray diffraction pattern of the transparent conductivethin film of the present invention, prepared in EXAMPLE 4.

FIG. 2 is an atomic force microscopic image of the transparentconductive thin film of the present invention, prepared in EXAMPLE 4.

FIG. 3 is an X-ray diffraction pattern of a transparent conductive thinfilm, prepared by the conventional technique in COMPARATIVE EXAMPLE 3.

FIG. 4 is an atomic force microscopic image of a transparent conductivethin film, prepared by the conventional technique in COMPARATIVE EXAMPLE3.

FIG. 5 is an X-ray diffraction pattern of a transparent conductive thinfilm, prepared by the conventional technique in COMPARATIVE EXAMPLE 5.

FIG. 6 is an atomic force microscopic image of a transparent conductivethin film, prepared by the conventional technique in COMPARATIVE EXAMPLE5.

FIG. 7 outlines one example of the organic EL device of the presentinvention.

NOTATION

-   1. Electrically insulating substrate-   2. Anode-   3. Cathode-   4. Transparent conductive thin film-   5. Metallic thin film-   6. Organic layer-   7. Light-emitting layer-   8. Hole-injecting layer-   9. Hole-transferring layer

DETAILED DESCRIPTION OF THE INVENTION

The transparent conductive thin film, process for producing the same,sintered target for producing the same, and transparent,electroconductive substrate for display panels and organicelectroluminescence devices, both including the transparent conductivethin film, are described in detail.

1. Thin, Transparent, Electroconductive Film

The transparent conductive thin film of the present invention comprisesindium oxide as the major component which contains either (1) silicon or(2) tungsten and germanium.

(1) Thin, Transparent, Electroconductive Film Containing Silicon

This transparent conductive thin film comprises indium oxide as themajor component which contains silicon as a dopant at a specificcontent, and has a substantially amorphous structure (this thin film ishereinafter referred to as the first, transparent conductive thin film).A transparent conductive thin film containing, in addition to silicon,tin and/or tungsten as a dopant at a specific content, is included inthe concept of the first, transparent conductive thin film.

The substantially amorphous structure for the present invention meansthat only halo pattern(s) relevant to the amorphous phase are observedbut no diffraction peak relevant to the crystalline phase is observed byX-ray diffractometry with the CuKα ray for investigating crystallinityof the film. Taking the crystalline phase of indium oxide as an example,it is important that no diffraction peak is observed at around 22, 31,35, 37, 46, 52 and 56° as 2θ.

A thin ITO film, i.e., thin, tin-doped indium oxide film, has been usedas a transparent conductive thin film for solar cells and variousdisplay panels. Its electroconductivity mechanism is explained asfollows. Tin tends to be transformed into the tetravalent ion to improveelectroconductivity of the film by releasing the carrier electrons whenit is dissolved after substituting for indium oxide at the trivalentindium ion site.

Moreover, oxygen deficiency tends to take place in indium oxide, andreleases the carrier electrons, when it takes place. Therefore, ITOneeds tin as a dopant and, at the same time, an adequate quantity ofoxygen deficiencies to have an increased carrier electron density.However, increasing oxygen deficiencies decreases carrier electronmobility. One method for minimizing electrical resistivity of the filmis use of another dopant element which, like tin, tends to take the formof tetra-valent ion and releases the carrier electrons when itsubstitutes for indium oxide at the trivalent indium site. One of thepromising elements for the above purpose is silicon.

The Sn⁴⁺ ion has a slightly smaller ionic radius than the In³⁺ ion, 0.71versus 0.81 Å. On the other hand, the Si⁴⁺ ion has a much smaller ionicradius of 0.41 Å than the In³⁺ ion. It is therefore considered thatsilicon strains the lattice to a higher extent than tin, to make thefilm amorphous more easily, when they are dissolved to substitute forindium oxide at the indium site.

In the present invention, therefore, silicon is used as a dopant inplace of tin, and incorporated at 0.5 to 13% by atom on silicon andindium totaled, preferably 1 to 12%, more preferably 3 to 11%, toimprove electroconductivity of the film. Silicon content beyond theabove range is not desirable, because the amorphous film may bedifficult to obtain at below 0.5% and resistivity of the film may beexcessively high at above 13%.

The transparent conductive thin film of the present invention, whichcomprises indium oxide as the major component and silicon as a dopant,may be further incorporated with tin. According to the above-describedelectroconductivity mechanism, this film is regarded as the thin ITOfilm, as the conventional transparent conductive thin film comprisingindium oxide as the major component and tin as a dopant, which isfurther incorporated with silicon.

Tin can improve electroconductivity of the film, when incorporated at0.5 to 15% by atom on tin and indium totaled, preferably 1 to 13%, morepreferably 3 to 10%. Tin content beyond the above range is notdesirable, because the amorphous film may be difficult to obtain atbelow 0.5% and resistivity of the film may be excessively high at above15%.

The transparent conductive thin film of indium oxide doped with siliconand tin is described above. Incorporating indium oxide with tungsten asa dopant can similarly contribute to improving electroconductivity ofthe film, because the tetra- to hexa-valent tungsten ion is dissolved tosubstitute for indium oxide at the tri-valent indium ion site and torelease the carrier electrons.

Therefore, tungsten can be incorporated for the present invention inindium oxide doped with silicon or silicon and tin, to produce the thin,amorphous, transparent, electroconductive film.

Tungsten can improve electroconductivity of the film, when incorporatedat 0.2 to 15% by atom on tungsten and indium totaled, preferably 1 to13%, more preferably 3 to 10%. Tungsten content beyond the above rangeis not desirable, because an amorphous film may be difficult to obtainat below 0.2% and resistivity of the film may be excessively high atabove 15%.

The first, transparent conductive thin film is structurally amorphous,and has a crystallization temperature of 180° C. or higher, preferably180 to 450° C. Crystallization temperature means the temperature levelat which the amorphous structure of the transparent conductive thin filmis crystallized, as judged by high-temperature X-ray diffractometry. Forthe present invention, it is the level at which the diffraction peakappears in the analysis in which the thin film is heated from roomtemperature at 3° C./minute.

The first, transparent conductive thin film of the present invention hasa resistivity of 9.0×10⁻⁴ Ω·cm or less, preferably 6.0×10⁻⁴ Ω·cm orless. It can have a resistivity of 3×10⁻⁴ Ω·cm or less, when thefilm-making conditions are optimized. By contrast, a conventionalamorphous ITO film has a resistivity limited to 6×10⁻⁴ Ω·cm to 8×10⁻⁴Ω·cm, and should be prepared by a special film-making process, asdiscussed earlier. A film having a resistivity above 9.0×10⁻⁴ Ω·cm isnot desirable, because the film should be thicker.

The first, transparent conductive thin film of the present invention hasa thickness of 100 to 500 nm, preferably 150 to 450 nm, more preferably200 to 400 nm. A film having a thickness beyond the above range is notdesirable, because it may not reliably have a sufficient resistivity atbelow 100 nm, and may encounter a problem of coloration at above 500 nm.

The transparent conductive thin film has a transmittance of 85% or morefor average visible rays (400 to 800 nm), preferably 90% or more, morepreferably 95% or more. A film having a transmittance below 85% may beinapplicable to an organic EL device.

The first, transparent conductive thin film of the present invention ischaracterized by its smooth surface. More specifically, it has anaverage centerline roughness (Ra) of 2.5 nm or less. The very smooth,thin film having a Ra value of 1.0 nm or less can be produced, when thefilm-making conditions are optimized.

The average centerline roughness (Ra) is determined by an atomic forcemicroscope. More specifically, the film is observed in an area of 1 by 1μm at 10 arbitrarily selected points on the film surface, and thereadings are averaged. A film having an Ra value above 2.5 nm is notdesirable, because it may be inapplicable to an organic EL electrodedirectly, and needs smoothening treatment by etching or grinding tosupport a superthin film of organic compound formed thereon.

(2) Thin, Transparent, Electroconductive Film Containing Tungsten andGermanium

This transparent conductive thin film comprises indium oxide as themajor component which contains tungsten and germanium as dopants at aspecific content (this thin film is hereinafter referred to as thesecond, transparent conductive thin film).

The second, transparent conductive thin film comprises indium oxide asthe major component and tungsten and germanium at a W/In atomic ratio of0.00.3 to 0.047 and Ge/In atomic ratio of 0.001 to 0.190. It isparticularly preferable that tungsten and germanium are incorporated ata W/In atomic ratio of 0.005 to 0.026 and Ge/In atomic ratio of 0.033 to0.190.

The second, transparent conductive thin film of the present inventionhas a resistivity of 8.0×10⁻⁴ Ω·cm or less, preferably 4.0×10⁻⁴ Ω·cm orless. It has an amorphous structure, as confirmed by X-raydiffractometry, crystallization temperature of 180° C. or lower, andsurface roughness Ra of 1.5 nm or less.

The second, transparent conductive thin film of the present invention isan In₂O₃—W—Ge-based one, comprising indium oxide as the major componentwhich contains tungsten and germanium as the second and third componentat a W/In atomic ratio of 0.003 to 0.047 and Ge/In atomic ratio of 0.001to 0.190. The thin film incorporated with tungsten and germanium each ata content in the above range can be produced by sputtering or ionplating on the substrate kept at a low temperature level of 150° C. orlower. It is of very low resistance, having a resistivity of 8.0×10⁻⁴Ω·cm or less, or 4.0×10⁻⁴ Ω·cm or less when the composition andfilm-making conditions are optimized. It is completely amorphous, andexcellent in surface smoothness with a surface roughness Ra (averagecenterline roughness) of 1.5 nm or less.

The present invention is preferably incorporated with tungsten andgermanium as the second and third component at a W/In atomic ratio of0.005 to 0.026 and Ge/In atomic ratio of 0.033 to 0.190. The thin filmincorporated with tungsten and germanium each at content in the aboverange can be produced by sputtering or ion plating on the substrate keptat 150 to 300° C. It is of very low resistance, having a resistivity of8.0×10⁻⁴ Ω·cm or less, or 4.0×10⁻⁴ Ω·cm or less when the composition andfilm-making conditions are optimized. It is completely amorphous, andexcellent in surface smoothness with a surface roughness Ra of 1.5 nm orless.

The second, transparent conductive thin film, having a crystallizationtemperature of 180° C. or higher, shows no deterioration of increasedresistivity or decreased surface roughness, even when exposed to a heatof 180° C. It is as excellent as ITO in transmittance of visible rays,including the low wavelength region. Tungsten or germanium present at aW/In or Ge/In atomic ratio beyond the above range is not desirable,because it may increase resistivity of the transparent conductive thinfilm or decrease its surface smoothness because it will be contaminatedwith the crystalline phase.

2. Sintered Target

The sintered target of the present invention comprises indium oxide asthe major component which contains either (1) silicon, or silicon andtin or tungsten, or (2) tungsten and germanium.

(1) Sintered Target Containing Silicon

The sintered target of the present invention containing silicon as adopant at a specific content (hereinafter referred to as the firstsintered target) is an indium oxide-based one, and can be a singletarget and composite target.

It is described while focusing on the composite targets with a pluralityof silicon chips put up, at almost the same intervals, on a sinteredtarget selected from the group consisting of sintered indium oxide,indium oxide doped with tin and indium oxide doped with tungsten as theexamples.

The composite sintered target of the present invention is produced byputting up a plurality of silicon chips, at almost the same intervals,on the erosion target surface, e.g., of indium oxide. This compositesintered target can contain silicon at a varying content in a desiredrange by changing surface area ratio of the silicon chips on thesintered target of indium oxide. Therefore, the effects of the filmcomposition or film-making conditions on amorphous degree or surfacesmoothness of the resulting transparent conductive thin film can beinvestigated in detail.

The sintered target of indium oxide serving as the base substantiallyconsists of indium oxide, by which is meant that it contains indiumoxide at 99.99% or more and essentially no impurities. The sinteredtarget of tin-doped or tungsten-doped indium oxide is the one made of atin-doped or tungsten-doped indium oxide sinter.

The indium oxide sinter, when incorporated with tin or tungsten as adopant, preferably contains tin at 0.5 to 15% by atom or tungsten at 0.2to 15% by atom (each on indium and the dopant totaled). It may befurther incorporated with molybdenum, rhenium, hafnium, germanium,zirconium, titanium, gold, silver, palladium, platinum or copper withinlimits not harmful to the object of the present invention.

The process for producing sintered indium oxide involves two majorsteps, where the starting powder is formed into a molded article in thefirst step, and the molded article is sintered in a furnace in thesecond step.

The step for forming the starting powder into a molded article usespowdered indium oxide as the starting powder, which may be incorporated,as required, with tin or tungsten oxide. The subsequent sintering stepinvolves a sub-step for setting the molded article on a furnace floorplate or setter in a furnace and subsequent sub-step for sintering thearticle in an oxygen atmosphere.

Powdered indium oxide as the starting powder has an average particlesize of 0.5 μm or less, preferably 0.4 μm or less, with a particle sizedistribution having the particles of 0.1 to 0.8 μm in size at 85% byweight or more, preferably 95% or more.

Tin or tungsten oxide, when used, preferably has an average particlesize of 2.5 μm or less as the starting powder. The starting powders canbe mixed with each other and stirred by a known apparatus. The mixturemay be granulated in the presence of a binder (PVA) or the like and thenadjusted to a particle size of 10 to 100 μm. The resulting granules arepressed at 1000 kg/cm² or more into a green body.

The type of the sintering furnace for the sintering step is not limited.However, it is normally an electrical heater because of its ease incontrolling the heated atmosphere. The green body is sintered at 1400°C. or higher for 1 hour or more, preferably 5 to 20 hours, in a furnaceequipped with a sufficient space for oxygen gas flow between the lowerside of the green body and the furnace floor plate and between the upperside of the green body and the ceiling plate, while the oxygen gas ispassed over the green body surfaces at 1000° C. or higher to replace theoxygen atmosphere in the furnace. On completion of the sintering step,flow of the oxygen gas is stopped, and the sinter is cooled. Thesintering step is controlled in such a way to keep temperaturefluctuation within the green body at 20° C. or lower.

The green body may be sintered in a flow of oxygen gas for less than 30minutes, when it is sufficiently small. However, the sintered target ofindium oxide has been recently becoming larger. A large body, e.g.,exceeding 300 mm square and 5 mm thick body, is more difficult tocontrol for its temperature distribution in the whole body, and it isrecommended to hold a body of that size in heat for preferably 60minutes or more.

The green body can be almost evenly sintered in both plane and thicknessdirections when heated for a sufficient time, to greatly controlscattering of sinter density and average hole number. Moreover, warp ofthe sinter resulting from uneven heating while it shrinks during thesintering process can be reduced by weight of the sinter itself.

The sintering process is followed by the cooling process, after heatingand flow of oxygen gas are stopped. The cooled sinter may be heatedagain at a sintering temperature (re-sintering).

The sinter thus produced may be machined by surface grinding or the liketo have the intended dimensions, and put up on a backing plate toproduce the composite target base. It may be of a divided structure, asrequired, with a plurality of the sinters.

The silicon chip is made of crystalline silicon, e.g.,single-crystalline or polycrystalline silicon, formed into a 1 to 10 mmsquare, 0.5 to 3 mm thick shape. The chip may be of an off-spec gradefor a semiconductor base board, in addition to the on-spec one normallyused for the board. The composite target of the present invention isproduced by putting up a plurality of the chips on the sintered targetof indium oxide, described earlier, at almost the same intervals.Silicon can be contained in the film at a varying content in a desiredrange by changing surface area ratio of the silicon chips on thesintered target of indium oxide.

The sintered target of the present invention has been described mainlywith the composite target. However, the situations around the singletarget are similar. It can be produced by incorporating silicon at aspecific content for the indium oxide sinter without needing any specialcondition.

The silicon is preferably produced from a starting powder of silicondioxide or the like having an average particle size of 2.5 μm or less.The starting powder can be mixed with indium oxide and stirred by aknown apparatus. The mixture may be granulated in the presence of abinder (PVA) or the like and then adjusted to a particle size of 10 to100 μm. The resulting granules are pressed at 1000 kg/cm² or more into agreen body, which is sintered in a similar manner.

(2) Sintered Target Containing Tungsten and Germanium

The second sintered target of the present invention comprises indiumoxide as the major component that necessarily contains tungsten andgermanium at a W/In atomic ratio of 0.003 to 0.045 and Ge/In atomicratio of 0.001 to 0.256. A sintered target containing tungsten orgermanium at a content beyond the above range may not give thetransparent conductive thin film even when the film-making conditionsare adjusted.

Tungsten and germanium as the second and third component for thesintered target are most preferably in the atomic state dissolved in andsubstituting for indium oxide at the indium site. However, they may bepresent in the form of indium germanide compound or tungstate compoundstate dispersed at the atomic level in the sintered body. Tungsten andgermanium, when so dispersed, are useful for producing the transparentconductive thin film of low resistance by working to stabilize dischargein the sputtering process. Tungsten and germanium are preferablydispersed substantially evenly. It is particularly preferable that nogermanium oxide phase is present.

The second sintered target of the present invention preferably has asurface roughness Rmax (maximum roughness) of 2.9 μm on the sputteredsurface. An oxide target, when sputtered for an extended time, hasabnormally grown projections (nodules) on the sputtered erosion surface,which may cause arcing or deterioration of film characteristics. Bycontrast, the second sintered target of the present invention shows nonodules on the erosion surface, even when sputtered for an extendedtime, by adjusting its surface roughness Rmax at 2.9 μm or less. As aresult, arcing can be prevented.

The surface roughness Rmax is a distance between the two straight linesrunning in parallel to the average line of a cross-sectional curved lineextracted to a standard length, coming into contact with the curved lineand putting the whole cross-sectional curved line in-between. Thestandard length is specified by JIS, which provides 6 standard lengthsby Rmax range. For example, the standard length is 0.8 mm for an Rmaxrange of 0.8 to 6.3 μm, and 2.5 mm for an Rmax range of 6.3 to 25 μm.The average line is a line (straight or curved) which representsgeometrical shape of the measured plane in the cross-sectional curvedline extracted and is set to have the minimum sum of squares of thedeviations between itself and the cross-sectional curved line.

3. Process for Producing Transparent Conductive Thin Film

The first and second, transparent conductive thin films of the presentinvention can be produced by sputtering or ion plating with the abovedescribed sintered target. When sputtering is adopted, the thin film canbe produced in an inert gas atmosphere containing a specific content ofoxygen in an apparatus which includes a substrate and the sinteredtarget of indium oxide doped with silicon, or tungsten and germanium.

The process for producing the first, transparent conductive thin film ofthe present invention produces a thin, amorphous, transparent,electroconductive film of silicon-doped indium oxide on a substrateunder specific sputtering conditions (e.g., substrate temperature,pressure, oxygen concentration) with the sintered target ofsilicon-doped indium oxide.

The present invention needs DC sputtering with a mixture of argon andoxygen, where oxygen gas should be present at 1% or more, preferably 1to 5%. Oxygen content beyond the above range is not desirable, becausethe resulting film may have insufficient transparency and deviatedcomposition resulting from the tendency of the dopant to leave thesurface when it is below 1%, and it may have an excessively highresistance when it is above 5%.

The amorphous film can be produced more easily and has higher surfacesmoothness when pressure in the sputtering apparatus is kept at 0.1 to 1Pa, in particular 0.3 to 0.8 Pa. Pressure beyond the above range is notdesirable, because it is more difficult to make the film amorphous atbelow 0.1 Pa, and more difficult to densify the film at above 1 Pa.

In the present invention, the film may be produced without heating thesubstrate. However, the amorphous film can be produced by heating thesubstrate at 100 to 300° C., in particular 100 to 200° C. The film ofthe present invention can be also produced by thermally treating thefilm at below crystallization temperature of the film in air, or aninert or vacuum atmosphere. This effect can be achieved by use of thesintered target of indium oxide containing silicon as the dopant, moreeffectively by use of the sintered target of indium oxide containingsilicon and tungsten as the dopants.

The thin film produced by this process, where indium oxide is doped withsilicon by DC sputtering effected under specific conditions, has moredistorted lattices than that of tin-doped ITO, with the result that itscrystallization temperature increases, making it easier to form theamorphous structure.

In other words, silicon strains the lattice, because Si⁴⁺ ion has asmaller ionic radius than the In³⁺ ion (0.39 versus 0.92 Å). Moreover,doping indium oxide with tungsten strengthens the In—O covalent bond,thereby stabilizing the amorphous structure. As a result, the amorphousstructure of the film can be kept stable, irrespective of film-makingconditions other than those described above. Tungsten also works todecrease resistivity of the film.

The conventional RF sputtering techniques have been described forproduction of the transparent conductive thin film of indium oxide dopedwith silicon and tin. However, the conventional RF sputtering techniquescannot stably produce a transparent conductive thin film of amorphousand flat/smooth structure.

The inventors of the present invention have attempted to produce atransparent conductive thin film by RF sputtering with a sintered targetof indium oxide doped with silicon oxide and pure argon gas, to findthat the resultant thin film is crystalline with very rough surfaces,even when the substrate is not heated. The similar trend was observedwhen the dopant was replaced by silicon oxide and tin oxide.

It is known that plasma generated by RF sputtering has generally muchhigher energy that that by DC sputtering. As a result, RF sputteringproduces a film of higher crystallinity. A highly crystalline film hasmuch rougher and less smooth surfaces, needless to say. Moreover, a thinoxide film having a large quantity of oxygen deficiencies will result,when produced by RF sputtering in an oxygen-free, pure argon gasatmosphere, because oxygen included in the film is limited to thatsupplied from the target.

The In—O bond in indium oxide that contains a larger quantity of oxygendeficiencies becomes more metallic, with the result that the crystalsgrow more easily in the film by the heat from the plasma during thefilm-making process. In other words, RF sputtering in an oxygen-free,pure argon gas atmosphere produces a highly crystalline film with veryrough surfaces, even when the substrate is not heated. It is thereforeconsidered that the essential conditions for producing an amorphous filmare the incorporation of silicon in the film and, at the same time, theuse of DC sputtering of low plasma energy with a sputtering gas ofargon/oxygen mixture containing oxygen at 1% or more.

A film of indium oxide doped with silicon or silicon and tin will becrystalline, when produced by RF sputtering with pure argon as asputtering gas. However, indium oxide doped with tungsten in addition tosilicon can be stably made into an amorphous film even under the aboveconditions.

Moreover, tungsten also works to decrease film resistivity.

The inventors of the present invention have confirmed that the In—O bondin indium oxide becomes more covalent in nature in the presence oftungsten by estimating its properties by the DV-Xα method for molecularorbit calculation. It is estimated that the film has a highercrystallization temperature as the In—O bond becomes more covalent. Thishas been also confirmed experimentally.

Crystallization temperature of an In₂O₃ film is around 150° C. It isincreased to around 200° C., when only tungsten is incorporated at 0.6%by atom, as confirmed by high-temperature X-ray diffractometry. It istherefore considered that indium oxide doped with tungsten in additionto silicon can be stably made into an amorphous film with smoothsurfaces.

Silicon-doped indium oxide can be made into a completely amorphous film,even when produced at a low gas pressure. It is made into an amorphousfilm more easily, when the substrate is heated. In other words, indiumoxide doped with a sufficient quantity of silicon, having an increasedcrystallization temperature, can be made into an amorphous film, evenwhen sputtering substantially increases substrate temperature or thesubstrate is intentionally heated, so long as the film is exposed to atemperature below the crystallization temperature determined by filmcomposition.

For the conventional ITO to be made into an amorphous film bysputtering, it is necessary to carry out the sputtering process under ahigh gas pressure to decrease energy of the sputtered particles, whilekeeping the substrate unheated. However, silicon-doped indium oxide forthe present invention can be made into a completely amorphous film evenunder a lower gas pressure. In other words, indium oxide doped with asufficient quantity of silicon, having an increased crystallizationtemperature, can be made into a film of amorphous structure, even whensputtering substantially increases substrate temperature or thesubstrate is intentionally heated, so long as the film is exposed to atemperature below the crystallization temperature determined by the filmcomposition.

The process for producing the second, transparent conductive thin filmof the present invention produces a thin, amorphous, transparent,electroconductive film on a substrate under specific sputteringconditions (e.g., substrate temperature, pressure, oxygen concentration)with the sintered target of indium oxide doped with tungsten andgermanium.

The second, transparent conductive thin film of the present inventioncan be produced by common sputtering or ion plating. When sputtering isadopted, compositional difference between the sintered target and thethin film with which it is produced depends on gas pressure, oxygencontent of sputtering gas, distance between the target and substrate,and magnetic field intensity in the plasma. In ion plating, thecompositional difference between the film and target also depends on gaspressure during the film-making process, and distance between the targetand substrate.

Sputtering, when adopted, needs DC sputtering with a mixture of argonand oxygen. It is important to have an oxygen content of 0.3% or more,preferably 0.5 to 5%. Oxygen content beyond the above range is notdesirable, because the resulting film may have insufficient transparencyand deviated composition resulting from tendency of the dopant to leavethe surface when it is below 0.3%, and may have an excessively highresistance when it is above 5%.

The amorphous film can be produced more easily and has higher surfacesmoothness when pressure in the sputtering apparatus is kept at 0.1 to 1Pa, in particular, at 0.3 to 0.8 Pa. Pressure beyond the above range isnot desirable, because it is more difficult to make the film amorphousat below 0.1 Pa, and more difficult to densify the film at above 1 Pa.

In the present invention, the film may be produced without heating thesubstrate. However, the amorphous film can be produced by heating thesubstrate at 100 to 300° C. The film of the present invention can bealso produced by thermally treating the film at below crystallizationtemperature of the film in air, or an inert or vacuum atmosphere.

The second, transparent conductive thin film of the present inventionproduced by this process, where indium oxide is doped with tungsten andgermanium by DC sputtering effected under specific conditions, has moredistorted lattices than that of tin-doped, with the result that itscrystallization temperature increases, making it easier to form theamorphous structure.

4. Transparent, Electroconductive Substrate for Display Panels

The transparent, electroconductive substrate of the present inventionfor display panels comprises the first or second, transparent conductivethin film formed on a substrate selected from the group consisting ofglass substrate, quartz plate and resin plate or film.

Display panels include LCD, PDP and EL devices. The transparent,electroconductive substrate of the present invention for display panelsincorporates the transparent conductive thin film that functions as theanode and/or cathode for the panel. The substrate also functions as alight-transmitting support, and hence should have a certain strength andtransparency.

The materials suitably used for constituting the resin plate or filmincludes polyethylene terephthalate (PET), polyether sulfone (PES),polyarylate and polycarbonate. The resin plates or films of thesematerials may be coated with an acrylic resin.

Thickness of the substrate is not limited. However, it is 0.5 to 10 mm,preferably 1 to 5 mm for the glass substrate or quartz plate, and 0.1 to5 mm, preferably 1 to 3 mm for the resin plate or film. Thickness beyondthe above range is not desirable, because the substrate may beinsufficient in strength and difficult to handle when it is thinner thanthe lower limit, and may be deteriorated in transparency and excessivelyheavy when it is thicker than the upper limit.

The substrate may be coated with at least one of an electricallyinsulating, semi-conductor, gas barrier or protective layer. Theelectrically insulating layer may be of silicon oxide (Si—O) or siliconoxynitride (Si—O—N). The semi-conductor layer may be of a thin-filmtransistor (TFT), and formed mainly on a glass substrate. The gasbarrier layer may be formed on a resin plate or film as a steam barrierlayer. The protective layer works to protect the substrate surface fromscratches or impact, and of a varying coating material, e.g., silicon-,titanium- or acrylic-based one. The layer which can be formed on thesubstrate is not limited to the above. For example, a thin,electroconductive, metallic layer may be also used.

The transparent, electroconductive substrate of the present inventionfor display panels is very useful as a part for various display panels,because it comprises a transparent conductive thin film excellent inresistivity, light transmittance and surface flatness, among otherfeatures.

5. Organic Electroluminescence Device

The organic electroluminescence device of the present inventioncomprises the first or second, transparent conductive thin film whichfunctions as the anode and/or cathode. It falls into two types: (A) adevice having a thin, light-reflecting film for the anode, and thetransparent conductive thin film for the cathode, where the film may becombined with a thin metallic film, and (B) a device having thetransparent, electroconductive substrate for display panels describedabove with the transparent conductive thin film serving as the cathode,where the substrate is coated with an organic layer and the anode.

FIG. 7 shows one example of the structure of the organicelectroluminescence device of the present invention. It has the anode 2and cathode 3, which hold in-between the organic layer 6 containing thelight-emitting layer 7. At least one of the anode 2 and cathode 3comprises the transparent conductive thin film 4 of the presentinvention, which may be combined with the thin metallic film 5.

The organic layer 6 may be of monolayer structure with thelight-emitting layer 7, which emits light produced by recombination ofthe holes and electrons supplied from the anode 2 and cathode 3,respectively. It may be also of a multi-layered structure (laminate)with the hole-injecting layer 8 and hole-transferring layer 9 or thelike. Moreover, it may be of a structure with the protective layer 11and electrically insulating layer 10 on the transparent conductive thinfilm 4 and substrate 1, respectively.

The organic layer 6, held between the anode 2 and cathode 3, providesvarious functions: (1) function of injecting holes from the anode 2 sideand electrons from the cathode 3 side, when put in an electrical field,(2) function of transferring the injected charges (electrons and holes)by an electrical field force, and (3) function of providing a field inthe light-emitting layer 7 for recombining the electrons and holes. Italso provides a light-emitting function by connecting these functions toeach other for emitting light.

Each of the hole-injecting layer 8 and hole-transferring layer 9 iscomposed of a hole-transferring compound, and function to transfer theholes, injected from the anode 2, to the light-emitting layer 7. A largequantity of the holes can be injected into the light-emitting layer 7 ata low electrical field in the presence of the hole-injecting layer 8 andhole-transferring layer 9 between the anode 2 and light-emitting layer7.

The cathode 3 is basically composed of the transparent conductive thinfilm 4 of the present invention. However, it may be of a two-layeredstructure (laminate) with the transparent conductive thin film 4 andthin, metallic layer 5. The thin, metallic layer 5 is provided to injectthe electrons more efficiently into the organic layer 6 containing thelight-emitting layer 7. The electrons to be injected from the cathode 3side into the light-emitting layer 7 are accumulated in thelight-emitting layer 7 at near the interface by the electron barrierpresent in the interface between the light-emitting layer 7 andhole-transferring layer 9, to improve light-emitting efficiency of theEL device. The thin, metallic layer 5 preferably has a lighttransmittance of 50% or more, more preferably 60% or more, to have atransparent light-emitting device. The thin, metallic layer 5 ispreferably superthin at around 0.5 to 20 nm. The thin, metallic layer 5is preferably of a metal having a work function of 3.8 eV or less. Thepreferable metals include Mg, Ca, Ba, Sr, Yb, Eu, Y, Sc, Li and alloysthereof.

On the other hand, the anode 2 is preferably an electroconductive metalhaving a work function of 4.4 eV or more, more preferably 4.8 eV ormore, or a transparent conductive thin film or laminate thereof. Theelectroconductive metals useful for the present invention may not benecessarily transparent, and may be coated with a black-colored carbonlayer or the like. The metals useful for the present invention includeAu, Pt, Ni, Pd, Cr and W. For the transparent conductive thin film, thetransparent conductive thin films of the present invention, the firstone (In—Si—O, In—Si—Sn—O, In—Si—W—O or In—Si—Sn—W—O) and the second one(In—W—Ge—O) are useful, needless to say. The anode that uses thetransparent conductive thin film of the present invention corresponds tothe thin, transparent, electroconductive substrate for display panels,which is provided with the substrate.

The laminates useful for the present invention include Au and In—Si—O,Pt and In—Si—O, In—Si—W—O and Pt, Au and In—W—Ge—O, and Pt andIn—W—Ge—O. The anode may be of a two-layered structure with anelectroconductive layer having a work function of 4.8 eV or less on theside opposite to the organic layer, because the anode can perform itsfunction when it has a work function of 4.8 eV or more on the interfacewith the organic layer. In this case, the useful materials for theelectroconductive layer include metals, e.g., Al, Ta and Nb; and alloys,e.g., Al and Ta—W. They also include electroconductive polymers, e.g.,doped polyaniline and polyphenylene vinylene; amorphous semiconductors,e.g., a-Si, a-SiC and a-C. Still more, they include black,semi-conductive oxides, e.g., Cr₂O₃, Pr₂O₅, NiO, Mn₂O₅ and MnO₂.

(A) Organic EL Device having a Thin, Light-reflecting Film for theAnode, and the Transparent Conductive Thin Film for the Cathode

This type is one of the preferred embodiments of the EL device of thepresent invention. Referring to FIG. 7, this EL device uses a thin,light-reflecting film (e.g., of chromium) for the anode 2, and thetransparent conductive thin film 4 of the present invention for thecathode 3, where the transparent conductive thin film 4 may be combinedwith the thin, metallic layer 5. This EL device can efficiently emitlight mainly from the cathode 3 side, because the cathode 3 is composedof the transparent conductive thin film 4 of the present invention.

(B) Organic EL Device Having the Transparent, ElectroconductiveSubstrate Serving as the Cathode, which is coated with an organic layerand the Anode.

This type of EL device emits light from the transparent substrate side.It has the transparent, electroconductive substrate for display panelswith the transparent conductive thin film formed on the transparent,electrically insulating substrate 1, which is coated with the anode 2and organic layer 6 or the like. The transparent, electricallyinsulating substrate 1 may be of glass, or resin film coated with abarrier film, e.g., steam barrier film of resin, silicon oxide orsilicon oxynitride.

The organic EL device of the present invention is characterized by highaverage luminance during the initial stage and long half-life ofluminance.

EXAMPLES

The present invention is described in detail by EXAMPLES, which by nomeans limit the present invention.

Properties of the transparent conductive thin film were determined bythe following procedures.

(1) The composition of the transparent conductive thin film wasdetermined by ICP emission spectroscopy for the film prepared in thesame manner as that for the present invention, except that quartz glasswas replaced by polyimide film for the substrate. The polyimide film wassubstantially free of silicon, indium, tin, tungsten or germaniumelement, as confirmed by ICP emission spectroscopy.(2) The crystallinity of the thin film was analyzed by X-raydiffractometry with CuKα ray, transmission electron microscopy andelectron diffractometry.(3) The crystallization temperature of the thin film was determined byhigh-temperature X-ray diffractometry. The film was analyzed by X-raydiffractometry while it was heated from room temperature at 3°C./minute. The temperature level at which a diffraction peak appearedwas judged to be its crystallization temperature.(4) The resistivity of the transparent conductive thin film was measuredby the 4-probe method, and the light transmittance of the film,including the substrate, was determined by spectrophotometry.(5) The average centerline roughness (Ra) of the film surface wasdetermined by an atomic force microscope, where the film was observed inan area of 1 by 1 μm at 10 arbitrarily selected points on the filmsurface, and the readings were averaged.

Examples 1 to 6

Powdered In₂O₃ (purity: 99.99%) was pressed and fired at 1400° C. toprepare an indium oxide sinter. It was formed into a shape, 6 in. indiameter and 5 mm thick, and put up on a backing plate of oxygen-freecopper via an In-based alloy, to prepare a target of In₂O₃. Chips of99.99% pure single-crystalline silicon, 1 by 1 by 0.5 mm or 2 by 2 by 1mm in size, were placed at the same intervals on the erosion surface ofthe target, to prepare a composite target.

A transparent conductive thin film, about 100 to 300 nm thick wasprepared by the following procedure. The above target for sputtering wasset on a cathode for the non-magnetic target in a DC magnetronsputtering apparatus, and a quartz glass substrate, 50 by 50 by 1.0 mmin size, was set in such a way to face the target, 70 mm apart. Ar gas(purity: 99.9999% by weight) was passed into the chamber when degree ofvacuum reached 1×10⁻⁴ Pa or less in the chamber. Oxygen was passed intothe film-making gas to obtain 1 to 3% of oxygen in the gas, while thechamber was kept at 0.6 Pa. DC power of 100 to 200 W was applied to thetarget-substrate space to produce DC plasma for sputtering, while thesubstrate was kept at room temperature.

The thin indium oxide film of varying silicon content was prepared withthe composite target of varying number of single-crystalline chips onthe In₂O₃ target. The resistivity and visible light transmittance of thefilm varied with the oxygen content of the sputtering gas. Compositionand surface roughness were analyzed in detail for the film showing thelowest resistivity while keeping visible light transmittance of at least80% in each EXAMPLE.

FIGS. 1 and 2 show an X-ray diffraction pattern and atomic forcemicroscopic image of the film prepared in EXAMPLE 4, respectively. Table1 gives Si atom content (silicon ratio to silicon and indium totaled),resistivity, crystallinity and surface roughness Ra (averaged) of thefilm prepared in each EXAMPLE. X-ray diffractometry detected no peak at22, 31, 35, 37, 46, 52 or 56° as 2θ.

TABLE 1 Si atom content Substrate Surface EXAM- of the temperatureResistivity roughness PLE film (%) (° C.) (Ω · cm) Crystallinity Ra 10.5 25 5.6 × 10⁻⁴ Amorphous 2.48 2 2.3 100 4.2 × 10⁻⁴ Amorphous 2.10 35.2 100 4.6 × 10⁻⁴ Amorphous 1.23 4 7.4 100 4.8 × 10⁻⁴ Amorphous 0.94 510.5 200 6.5 × 10⁻⁴ Amorphous 0.95 6 13.0 300 8.8 × 10⁻⁴ Amorphous 1.25

As shown in Table 1, indium oxide doped with silicon at a contentspecified for the present invention was kept amorphous, when made into afilm by sputtering even at a low gas pressure of 0.6 Pa with thesubstrate heated at 100 to 300° C. The films had a low resistivity of8.8×10⁻⁴ Ω·cm or less, mostly 6.0×10⁻⁴ Ω·cm or less. Average centerlinesurface roughness Ra, determined by atomic force microscopy, was verylow at 2.48 nm or less for all of the films analyzed. Average visiblelight transmittance of the film (including the substrate) was also highat 85 to 90%. Crystallinity of the amorphous, transparent conductivethin films prepared in EXAMPLES 1 to 6 was 190 to 390° C., as determinedby high-temperature X-ray diffractometry.

The films were also prepared in the same manner as in EXAMPLES 1 to 6,except that the composite target was replaced by a single sinteredtarget of silicon-doped indium oxide. For production of the sinteredtarget of silicon-doped indium oxide, a mixture of powdered indium andsilicon oxide (starting powder) was prepared, pressed, fired and thenground. DC sputtering was carried out in an argon/oxygen mixture gascontaining oxygen at 1 to 3% with the above target and substrate kept atvarying temperature from room temperature to 300° C. The evaluationresults of these films were almost the same as those given in Table 1.It is therefore found that an amorphous film of excellent surfacesmoothness and low resistivity can be produced not only with thecomposite target containing the chips but also with the sintered targetof silicon-doped indium oxide.

Examples 7 to 22

The composite target was prepared using a sintered target of indiumoxide doped with tin of varying content (i.e., ITO), in place of theindium oxide target, and placing chips of single-crystalline silicon atthe same intervals immediately above the erosion surface of the target.It was 6 in. in diameter and 5 mm thick, as before.

The thin films of indium oxide doped with tin and silicon, about 100 to300 nm thick, were prepared in a manner similar to those for EXAMPLES 1to 6, where oxygen content of the sputtering gas was kept at 1 to 3%.Composition and surface roughness were analyzed for the film showing thelowest resistivity while keeping visible light transmittance of at least80% in each EXAMPLE. Table 2 gives Sn atom content (tin ratio to indiumand tin totaled), Si atom content (silicon ratio to silicon and indiumtotaled), resistivity, crystallinity and average centerline surfaceroughness (Ra) of the film prepared in each EXAMPLE analyzed in asimilar manner.

TABLE 2 Sn atom Si atom content content Substrate Surface of the of thetemperature Resistivity roughness EXAMPLE film (%) film (%) (° C.) (Ω ·cm) Crystallinity Ra 7 0.5 1.1 25 5.0 × 10⁻⁴ Amorphous 2.30 8 1.2 5.4100 5.2 × 10⁻⁴ Amorphous 2.42 9 3.5 3.5 200 3.8 × 10⁻⁴ Amorphous 2.21 103.4 7.5 200 3.5 × 10⁻⁴ Amorphous 2.10 11 3.5 10.2 200 4.0 × 10⁻⁴Amorphous 2.05 12 3.8 12.5 200 4.5 × 10⁻⁴ Amorphous 2.32 13 7.4 1.2 255.6 × 10⁻⁴ Amorphous 1.95 14 7.7 3.2 100 3.5 × 10⁻⁴ Amorphous 1.98 157.5 7.5 200 4.6 × 10⁻⁴ Amorphous 1.85 16 7.6 10.5 200 5.2 × 10⁻⁴Amorphous 1.75 17 7.4 12.6 200 5.4 × 10⁻⁴ Amorphous 1.85 18 10.3 3.0 1005.5 × 10⁻⁴ Amorphous 0.95 19 10.1 8.0 200 5.6 × 10⁻⁴ Amorphous 0.85 2010.5 9.0 200 5.8 × 10⁻⁴ Amorphous 0.87 21 14.9 2.0 100 5.5 × 10⁻⁴Amorphous 1.12 22 15.0 12.0 300 5.7 × 10⁻⁴ Amorphous 1.25

As shown in Table 2, indium oxide doped with silicon and tin, each at acontent specified for the present invention, was kept amorphous, whenmade into a film by sputtering even at 200° C. Resistivity was low at5.8×10⁻⁴ Ω·cm or less. Average centerline surface roughness (Ra),determined by atomic force microscopy, was very low at 2.42 or less.Average visible light transmittance of the film (including thesubstrate) was also high at 84 to 90%. The crystallinity of theamorphous, transparent conductive thin films prepared in EXAMPLES 7 to22 was 180 to 320° C., as determined by high-temperature X-raydiffractometry.

The films were also prepared in the same manner as in EXAMPLES 7 to 22,except that the composite target was replaced by a single sinteredtarget of indium oxide doped with silicon and tin element. Forproduction of the sintered target of indium oxide doped with silicon andtin, a mixture of powdered indium oxide, silicon oxide and tin oxide(starting powder) was prepared, pressed, fired and then ground. DCsputtering was carried out in an argon/oxygen mixture gas containingoxygen at 1 to 3% with the above target and substrate kept at varyingtemperature from room temperature to 300° C. The evaluation results ofthese films were almost the same as those given in Table 2. It istherefore found that an amorphous film of excellent surface smoothnessand low resistivity can be produced not only with the composite targetcontaining the chips but also with the sintered target of indium oxidedoped with silicon and tin elements.

Examples 23 to 42

The composite target was prepared using a sintered target of indiumoxide doped with tungsten of varying content, in place of the indiumoxide target, and placing chips of single-crystalline silicon at thesame intervals on the erosion surface of the target. It was 6 in. indiameter and 5 mm thick as before.

The thin films of indium oxide doped with tungsten and silicon, about100 to 300 nm thick, were prepared in a manner similar to those forEXAMPLES described above, where oxygen content of the sputtering gas waskept at 1 to 3%. Composition and surface roughness were analyzed for thefilm showing the lowest resistivity while keeping visible lighttransmittance of at least 80% in each EXAMPLE. Table 3 gives W atomcontent (tungsten ratio to tungsten and indium totaled), Si atom content(silicon ratio to silicon and indium totaled), resistivity,crystallinity and average centerline surface roughness (Ra) of the filmprepared in each EXAMPLE, analyzed in a similar manner.

TABLE 3 W atom Si atom content of content of Substrate Surface the filmthe film temperature Resistivity roughness EXAMPLE (%) (%) (° C.) (Ω ·cm) Crystallinity Ra 23 0.2 1.0 25 7.8 × 10⁻⁴ Amorphous 2.46 24 0.4 1.125 3.8 × 10⁻⁴ Amorphous 2.41 25 0.6 1.1 25 3.8 × 10⁻⁴ Amorphous 2.41 260.6 2.3 25 4.5 × 10⁻⁴ Amorphous 0.89 27 0.6 2.4 100 3.3 × 10⁻⁴ Amorphous0.51 28 1.1 5.0 100 4.2 × 10⁻⁴ Amorphous 2.25 29 3.2 3.1 100 3.4 × 10⁻⁴Amorphous 2.21 30 3.1 7.7 200 4.5 × 10⁻⁴ Amorphous 1.90 31 3.0 10.2 2004.7 × 10⁻⁴ Amorphous 2.23 32 3.3 12.5 200 4.3 × 10⁻⁴ Amorphous 2.31 337.1 1.1 25 5.6 × 10⁻⁴ Amorphous 2.22 34 7.2 3.7 100 3.4 × 10⁻⁴ Amorphous1.72 35 7.1 6.0 200 4.7 × 10⁻⁴ Amorphous 2.35 36 7.5 10.0 200 4.2 × 10⁻⁴Amorphous 1.55 37 7.4 12.8 200 5.2 × 10⁻⁴ Amorphous 1.75 38 11.1 3.5 1005.5 × 10⁻⁴ Amorphous 1.95 39 11.5 5.3 200 5.3 × 10⁻⁴ Amorphous 1.67 4011.5 9.9 200 5.5 × 10⁻⁴ Amorphous 1.54 41 13.9 2.3 100 5.1 × 10⁻⁴Amorphous 1.30 42 14.9 11.9 300 4.3 × 10⁻⁴ Amorphous 1.16

As shown in Table 3, indium oxide doped with silicon and tungsten eachat a content specified for the present invention was kept amorphous,when made into a film by sputtering even at 300° C. Resistivity was lowat 5.6×10⁻⁴ Ω·cm or less. Average centerline surface roughness (Ra),determined by atomic force microscopy, was very low at 2.41 or less.Average visible light transmittance of the film (including thesubstrate) was also high at 85 to 90%. Crystallinity of the amorphous,transparent conductive thin films prepared in EXAMPLES 23 to 42 was 180to 450° C., as determined by high-temperature X-ray diffractometry.

The films prepared in EXAMPLES 1 to 42 were measured for their etchingcharacteristics with a weakly acidic etchant. Their etchingcharacteristics were good, because all of the films could be etched at ahigh rate leaving no etching-caused residue.

The films were also prepared in the same manner as in EXAMPLES 23 to 42,except that the composite target was replaced by a single sinteredtarget of indium oxide doped with silicon and tungsten element. Forproduction of the sintered target of indium oxide doped with silicon andtungsten, a mixture of powdered indium oxide, silicon oxide and tungstenoxide (starting powder) was prepared, pressed, fired and then ground. DCsputtering was carried out in an argon/oxygen mixture gas containingoxygen at 1 to 3% with the above target and substrate kept at varyingtemperature from room temperature to 300° C. The evaluation results ofthese films were almost the same as those given in Table 3. It istherefore found that an amorphous film of excellent surface smoothnessand low resistivity can be produced not only with the composite targetcontaining the chips but also with the sintered target of indium oxidedoped with silicon and tungsten element.

Comparative Examples 1 to 6

Thin films, about 100 to 300 nm thick, were prepared by sputtering witha sintered target of impurity-free indium oxide or tin-doped indiumoxide (ITO), both having been used widely. Gas pressure during thesputtering process, target-substrate distance and target size were thesame as those for the EXAMPLES described above. The oxygen content ofthe sputtering gas was kept at 1 to 3%. The composition and surfaceroughness were analyzed for the film showing the lowest resistivitywhile keeping visible light transmittance of at least 80% in eachCOMPARATIVE EXAMPLE. Table 4 gives the Sn atom content (tin ratio toindium and tin totaled), resistivity, crystallinity and averagecenterline surface roughness (Ra) of the film prepared in eachCOMPARATIVE EXAMPLE, analyzed in a similar manner.

TABLE 4 Sn atom content Substrate COMPARATIVE of the temperatureResistivity Surface EXAMPLE film (%) (° C.) (Ω · cm) Crystallinityroughness Ra 1 0 25 4.0 × 10⁻³ Amorphous/ 5.34 crystalline mixture 2 0100 3.8 × 10⁻³ Crystalline 8.84 3 4.5 25 5.2 × 10⁻⁴ Amorphous/ 5.54crystalline mixture 4 4.6 200 4.5 × 10⁻⁴ Crystalline 7.95 5 7.5 200 2.5× 10⁻⁴ Crystalline 8.45 6 14.8 200 5.6 × 10⁻⁴ Crystalline 9.51

As shown in Table 4, the thin films prepared in COMPARATIVE EXAMPLES 1to 6 always contain the crystalline phase detected by X-raydiffractometry, although low in resistivity at 2.5×10⁻⁴ to 5.6×10⁻⁴Ω·cm. FIGS. 3 and 4 show an X-ray pattern and atomic force microscopicimage of the film prepared in COMPARATIVE EXAMPLE 3, respectively, wherethe film contained both amorphous and crystalline phases. FIGS. 5 and 6show an X-ray pattern and atomic force microscopic image of the filmprepared in COMPARATIVE EXAMPLE 5, respectively, where the film wascomposed of the crystalline phases. X-ray diffractometry detected alarge peak at one of 22, 31, 35, 37, 46, 52 or 56° as 2θ.

These films had a notably higher average centerline roughness (Ra) of5.3 nm or more than those of the present invention, prepared in EXAMPLES1 to 22. They had also a high resistivity, and contained a finecrystalline phase, even when prepared by sputtering without heating thesubstrate. They were composed of a mixture of an amorphous andcrystalline phase.

These films were measured for their etching characteristics with aweakly acidic etchant under the same conditions as those for theEXAMPLES. It was found that they tended to leave etching-caused residueof the crystalline phase, and were etched at a lower rate, taking 1.5 to2 times longer time than those prepared in the EXAMPLES.

These results indicate that it is necessary to grind these films toremove surface roughness when they are to be used for transparentelectrodes for LCD and organic EL devices.

Examples 43 to 70

A In₂O₃—W—Ge-based, sintered target, comprising indium oxide as themajor component and tungsten and germanium was prepared by the followingprocedure, where the W/In and Ge/In atomic ratios in the target wasvaried at levels given in Table 5. The starting powder comprisedpowdered In₂O₃, WO₃ and GeO₂, each having an average particle size of 1μm or less.

A mixture of given quantities of powdered In₂O₃, WO₃ and GeO₂ wasball-milled in a resin pot with water and balls of hard ZrO₂ for 20hours. The resulting mixed slurry was filtered, dried and granulated.The granules were molded in a mold by cold isostatic pressing at 3tons/cm² into an intended shape.

Next, the above molded article was held at 1200° C. for 5 hours in asintering furnace in an oxygen atmosphere flowing at 5 L/minute per 0.1m³ of the furnace inside volume, where it was heated at 1° C./minute upto 1000° C. and at 3° C./minute from 1000 to 1200° C. Then, the oxygenflow was stopped, and the resulting sinter was allowed to cool at 10°C./minute from 1200 to 1000° C. Finally, it was held at 1000° C. for 3hours in an Ar atmosphere flowing at 10 L/minute per 0.1 m³ of thefurnace inside volume, and then it was left to stand and cooled to roomtemperature.

The density of the resulting sinter was determined by the Archimedeanmethod, and converted into relative density based on the theoreticaldensity. The theoretical density was found by dividing the weight of theunit lattice by the volume of the unit lattice, where the former wasdetermined on the assumption that the analyzed quantities of W and Gewere totally dissolved in and substituted for the In₂O₃ crystal free ofoxygen defects (bixbite type structure) at the In site, and the latterwas determined from the lattice constants found by X-ray diffractometry.Each sinter was found to have a relative density of 90% or more. ICPemission spectroscopy results confirmed that the analyzed W and Gecontent of the sinter were kept in agreement with those estimated fromthe charged quantities.

Each sinter was ground by a cup grindstone to have a surface roughnessRmax in a range of 2.2 to 2.7 μm, and cut into a shape, 152 mm indiameter and 5 mm thick, to prepare the sintered target. It was put upon a backing plate of oxygen-free copper via an In-based alloy, toprepare a sputtering target of the In₂O₃—W—Ge-based sinter.

The sputtering target was set on a cathode for non-magnetic target in aDC magnetron sputtering apparatus, and the substrate was set in such away to face the target 60 to 80 mm apart. The substrate was a 1 mm thicksynthetic quartz glass. Ar gas (purity: 99.9999% by weight) was passedinto the chamber, after it was evacuated to a vacuum degree of 1×10⁻⁴ Paor less, to a gas pressure of 0.6 Pa. Oxygen was passed into the Ar gasto 0.5 to 3%, while the chamber was kept at 0.6 Pa. A DC power of 150 to400 W was applied to the target-substrate space to produce a DC plasmafor sputtering, while the substrate was kept at room temperature (about25° C.) or heated at 300° C. or lower, in order to produce a transparentconductive thin film having a thickness of about 200 nm.

Table 5 shows compositions of each sintered target and transparentconductive thin film prepared by sputtering in the presence of thetarget, quantitatively determined by ICP emission spectroscopy, togetherwith W/In and Ge/In atomic ratios, and substrate temperature during thefilm-making process. Moreover, each transparent conductive thin film wasmeasured for its resistivity by the 4-probe method before and afterannealing at 180° C. in air, and surface roughness Ra. The results aregiven in Table 6.

TABLE 5 Target composition Base Film composition (atomic ratio)temperature (atomic ratio) EXAMPLE W/In Ge/In (° C.) W/In Ge/In 43 0.0030.012 Room 0.003 0.012 temperature 44 0.004 0.015 Room 0.004 0.015temperature 45 0.004 0.019 Room 0.004 0.019 temperature 46 0.003 0.057Room 0.003 0.057 temperature 47 0.006 0.001 Room 0.006 0.001 temperature48 0.006 0.012 Room 0.006 0.012 temperature 49 0.010 0.001 Room 0.0100.001 temperature 50 0.010 0.004 Room 0.010 0.004 temperature 51 0.0150.001 Room 0.015 0.001 temperature 52 0.030 0.005 120 0.030 0.005 530.030 0.010 120 0.030 0.010 54 0.045 0.150 120 0.046 0.150 55 0.0450.190 120 0.047 0.190 56 0.006 0.041 180 0.005 0.033 57 0.006 0.205 2500.006 0.150 58 0.006 0.256 300 0.005 0.186 59 0.012 0.042 180 0.0150.036 60 0.012 0.205 250 0.016 0.153 61 0.012 0.256 300 0.015 0.188 620.020 0.041 180 0.018 0.040 63 0.022 0.203 250 0.019 0.153 64 0.0210.255 300 0.018 0.188 65 0.025 0.041 180 0.023 0.035 66 0.025 0.205 2500.023 0.154 67 0.025 0.256 300 0.022 0.189 68 0.032 0.041 180 0.0240.037 69 0.032 0.205 250 0.025 0.155 70 0.032 0.256 300 0.026 0.190

TABLE 6 Film resistivity Film surface roughness (Ω · cm) Ra (nm) BeforeAfter Before After EXAMPLE annealing annealing annealing annealing 437.5 × 10⁻⁴ 7.8 × 10⁻⁴ 0.83 0.93 44 5.8 × 10⁻⁴ 6.2 × 10⁻⁴ 0.89 0.95 455.5 × 10⁻⁴ 5.9 × 10⁻⁴ 0.88 0.92 46 7.5 × 10⁻⁴ 7.9 × 10⁻⁴ 0.93 0.89 472.2 × 10⁻⁴ 2.5 × 10⁻⁴ 0.94 0.98 48 3.9 × 10⁻⁴ 4.3 × 10⁻⁴ 0.92 1.02 492.8 × 10⁻⁴ 3.5 × 10⁻⁴ 0.95 0.98 50 3.8 × 10⁻⁴ 4.2 × 10⁻⁴ 0.88 0.96 514.0 × 10⁻⁴ 4.5 × 10⁻⁴ 0.80 0.96 52 6.5 × 10⁻⁴ 7.1 × 10⁻⁴ 0.98 0.98 536.9 × 10⁻⁴ 7.3 × 10⁻⁴ 1.32 1.48 54 7.5 × 10⁻⁴ 8.0 × 10⁻⁴ 1.32 1.43 557.3 × 10⁻⁴ 7.9 × 10⁻⁴ 1.32 1.45 56 3.5 × 10⁻⁴ 3.7 × 10⁻⁴ 0.85 0.97 573.4 × 10⁻⁴ 3.8 × 10⁻⁴ 0.93 0.97 58 3.6 × 10⁻⁴ 3.9 × 10⁻⁴ 0.96 0.98 592.8 × 10⁻⁴ 3.2 × 10⁻⁴ 0.93 0.98 60 3.0 × 10⁻⁴ 3.3 × 10⁻⁴ 0.96 0.94 613.1 × 10⁻⁴ 3.5 × 10⁻⁴ 0.85 0.97 62 2.8 × 10⁻⁴ 2.9 × 10⁻⁴ 0.89 0.98 633.3 × 10⁻⁴ 3.4 × 10⁻⁴ 0.85 0.92 64 3.2 × 10⁻⁴ 3.5 × 10⁻⁴ 0.86 0.94 653.2 × 10⁻⁴ 3.5 × 10⁻⁴ 0.96 0.96 66 3.3 × 10⁻⁴ 3.4 × 10⁻⁴ 0.89 0.99 673.5 × 10⁻⁴ 3.6 × 10⁻⁴ 0.87 0.94 68 3.3 × 10⁻⁴ 3.9 × 10⁻⁴ 0.84 0.93 693.4 × 10⁻⁴ 3.8 × 10⁻⁴ 0.89 0.98 70 3.5 × 10⁻⁴ 4.0 × 10⁻⁴ 0.83 0.98

Comparative Examples 7 to 14

Thin, transparent, electroconductive films were prepared, whichcomprised In₂O₃ doped only with W or Ge, or doped with W and Gesimultaneously but at a W/In and Ge/In atomic ratio out of the range forthe present invention. In other words, the sintered target containing Wor Ge at a varying W/In or Ge/In atomic ratio was prepared (Table 7) inthe same manner as in EXAMPLES. ICP emission spectroscopy resultsconfirmed that the analyzed W and Ge content of the sinter were kept inagreement with those estimated from the charged quantities. Next, eachsinter was formed into the sputtering target also in the same manner.The transparent conductive thin film having a thickness of about 200 nmwas prepared with the above target on the same substrate under the sameconditions as in EXAMPLES.

These sintered targets and sputtering-prepared transparent conductivethin films prepared in COMPARATIVE EXAMPLES 7 to 14 were similarlymeasured for their compositions, and the resultant transparentconductive thin films for their resistivity and surface roughness Ra.Table 7 gives compositions and substrate temperature during thesputtering process for the sintered targets and transparent conductivethin films, and Table 8 gives resistivity and surface roughness Ra ofthe resulting transparent conductive thin films.

TABLE 7 Target composition Base Film composition COMPARATIVE (atomicratio) temperature (atomic ratio) EXAMPLE W/In Ge/In (° C.) W/In Ge/In 7— 0.041 Room — 0.035 temperature 8 — 0.076 Room — 0.062 temperature 9 —0.205 Room — 0.157 temperature 10 — 0.256 Room — 0.190 temperature 11 —0.041 180 — 0.037 12 — 0.256 300 — 0.201 13 0.002 0.001 Room 0.002 0.100temperature 14 0.003 — Room 0.003 — temperature

TABLE 8 Film resistivity Film surface (Ω · cm) roughness COMPARATIVEBefore After Before After EXAMPLE annealing annealing annealingannealing  7 8.5 × 10⁻⁴ 1.3 × 10⁻³ 1.65 1.98  8 7.5 × 10⁻⁴ 9.1 × 10⁻⁴1.75 1.99  9 6.3 × 10⁻⁴ 7.9 × 10⁻⁴ 2.41 2.56 10 5.9 × 10⁻⁴ 9.3 × 10⁻⁴2.65 2.98 11 5.1 × 10⁻⁴ 7.5 × 10⁻⁴ 1.54 2.03 12 4.9 × 10⁻⁴ 5.5 × 10⁻⁴1.75 1.99 13 8.5 × 10⁻⁴ 9.6 × 10⁻⁴ 3.50 4.10 14 8.7 × 10⁻⁴ 9.5 × 10⁻⁴2.70 3.50

As shown in Tables 5 and 6, each of the transparent conductive thinfilms of the present invention contained W and Ge at a W/In and Ge/Inatomic ratio of 0.003 to 0.047 and 0.001 to 0.190, respectively. Each ofthe films formed on the substrate kept at room temperature (thoseprepared in EXAMPLES 43 to 51) had a low resistivity of 8.0×10⁻⁴ Ω·cm orless, amorphous structure as confirmed by X-ray diffractometry, andsurface roughness Ra of 1.0 nm or less determined by atomic forcemicroscopy. These films had the characteristics essentially remainingunchanged even when exposed to an annealing heat of 180° C.

Each of the transparent conductive thin films formed on the substratekept at 150 to 300° C. (those prepared in EXAMPLES 52 to 70) also had alow resistivity of 8.0×10⁻⁴ Ω·cm or less, amorphous structure asconfirmed by X-ray diffractometry, and surface roughness Ra of 1.5 nm orless determined by atomic force microscopy. Particularly noted were thefilms formed on the substrate kept at 180 to 300° C. (those prepared inEXAMPLES 56 to 70) had a low resistivity of 4.0×10⁻⁴ Ω·cm or less, whilekeeping good surface smoothness. All of these films had thecharacteristics essentially remaining unchanged even when exposed to anannealing heat of 180° C.

On the other hand, the transparent conductive thin films prepared inCOMPARATIVE EXAMPLES 7 to 14, which were free of W or Ge, or contained Wand Ge simultaneously but at a W/In and Ge/In atomic ratio out of therange for the present invention, had a surface roughness of 1.5 nm ormore. Moreover, their characteristics were greatly changed by annealingheat of 180° C. Those prepared in COMPARATIVE EXAMPLES 8 to 12 had agreatly increased resistivity when exposed to an annealing heat of 180°C., although it was 8.0×10⁻⁴ Ωcm or less before annealing.

The light transmittance of the transparent conductive thin films of thepresent invention was determined by spectrophotometry. As a result, theywere found to have an average visible rays transmittance of 89 to 91%. Athin film of In₂O₃—ZnO containing ZnO at 10% by weight was preparedseparately in the same manner as in the EXAMPLES on the same substrateto the same thickness, and its light transmittance was compared withthat of the film of the present invention. The transparent conductivethin films of the present invention were found to have an apparentlyhigher transmittance in the short wavelength region (e.g., 400 nm) ofvisible rays than the In₂O₃ ZnO-based one.

The transparent conductive thin film was prepared in the same manner asin the EXAMPLES, except that substrate was replaced by a polyethersulfone (PES) film coated with 1 μm thick acrylic-based hard coat layer(total thickness: 0.2 mm), which was further coated with a 50 nm thicksilicon oxynitride film. Each of the transparent conductive thin filmsformed on the substrate, which also fall into the scope of the presentinvention, was confirmed to have almost the same characteristics asthose of prepared in EXAMPLES 43 to 55 having the same composition.

Comparative Example 15

A thin film, about 200 nm thick, was prepared in the same manner as inthe EXAMPLES on the same, except that the target was replaced by asintered target of In₂O₃ doped with 5% by weight of SnO₂ (ITO), whichhas been used for the conventional target. The sintered ITO had arelative density of 98% and Sn content, determined by emissionspectroscopy, in agreement with that estimated from the charged quantityfor preparing the starting powder mixture. The ITO-based, transparentconductive thin film had a much higher resistivity of 8.5×10⁻⁴ Ω·cm thanthe transparent conductive thin film of the present invention. It wasamorphous, but, when annealed in air at 180° C., had a resistivitygreatly decreased to 3.5×10⁻⁴ Ω·cm, and it transformed into acrystalline phase to have much rougher surface.

Examples 71 to 75

The In₂O₃—W—Ge-based sinter containing W and Ge at a W/In and Ge/Inatomic ratio of 0.032 and 0.205 was prepared, and ground by a varyingcup grindstone to prepare the sintered target having a varying surfaceroughness Rmax of 1.5 to 4.9.

Each of the targets prepared in EXAMPLES 71 to 75 was set on a cathodefor the non-magnetic target in a DC magnetron sputtering apparatus, aswas the case with the one for EXAMPLES 43 to 70. The transparentconductive thin film was prepared by continuous sputtering in thepresence of a DC plasma with each target following the procedure similarto those for EXAMPLES 43 to 70 under the film-making conditions oftarget-substrate distance: 60 mm, Ar gas purity: 99.9999% by weight, gaspressure: 0.5 Pa, and DC power used:500 W.

The cumulative power consumed for the continuous sputtering processuntil an arcing phenomenon was observed, and the maximum erosion depth(depth from the plane opposite to the sputtered plane) when the arcingwas started was measured. The observations were used to establish therelationship between the surface roughness Rmax and arcing conditions.The results are given in Table 9.

TABLE 9 Surface roughness Rmax Maximum erosion depth of the sputteredtarget when the arcing was surface (μm) started (mm) EXAMPLE 71 1.5 Notobserved during the testing period 72 2.0 Not observed during thetesting period 73 2.1 Not observed during the testing period 74 2.5 Notobserved during the testing period 75 2.9 Not observed during thetesting period COMPARATIVE EXAMPLE 16 3.3 Arcing started at 4.5 mm 173.6 Arcing started at 3.7 mm 18 4.3 Arcing started at 2.6 mm 19 4.9Arcing started at 1.8 mm

As shown in Table 9, the sintered targets of EXAMPLES 71 to 75 showedneither arcing nor black-colored projections thereon throughout thecontinuous sputtering process, even when cumulative power increased.Therefore, each of these targets was serviceable throughout the testingperiod. The film-making rate and film characteristic test resultsindicated that each of the targets of EXAMPLES 71 to 75 kept the initialcharacteristics even when cumulative power increased, showing adesirable low resistivity and high transmittance throughout the testingperiod. The transparent conductive thin film prepared with any of thesintered targets prepared in EXAMPLES 71 to 75 following the proceduresimilar to those for EXAMPLES 43 to 70 showed constant, excellentcharacteristics throughout the testing period, irrespective offilm-making time and cumulative power consumed. The same trend wasobserved with the sintered targets containing W and Ge at a W/In andGe/In atomic ratio of 0.003 to 0.045 and 0.001 to 0.256, respectively.

Comparative Examples 16 to 19

On the other hand, the continuous sputtering was carried out in theseexamples in the same manner as in EXAMPLES 71 to 75, except that thesintered target had a surface roughness Rmax on the sputtered planeexceeding 2.9. Arcing was observed with each target as cumulative powerincreased to massively produce black projections on the surface, asshown in Table 9. The film prepared after the arcing phenomenon wasnotably observed having a resistivity and visible light transmittancegreatly deteriorated as compared with that prepared before thephenomenon was not observed. Therefore, the deteriorated sinter couldnot be used as it was. An organic EL device with the electrode of thetransparent conductive thin film prepared after arcing was massivelyobserved showing notably deteriorated luminance.

Example 76

The organic EL device of the present invention was prepared by thefollowing procedure. It had a laminate of thin In—W—Si—O-based andMg—Ag-based films for the cathode, and chromium for the anode. A 200 nmthick Cr film was formed on a glass substrate by DC sputtering with a Crtarget having a diameter of 6 inches under the conditions of sputteringgas: Ar, pressure: 0.4 Pa and DC power: 300 W. The Cr film was patternedby the common lithography technique, to have the anode of a given shapethereon.

Next, the glass substrate coated with the Cr anode was further coatedwith a 200 nm thick electrically insulating layer of silicon dioxide(SiO₂) by oxygen-reactive sputtering with a Si target. This insulatinglayer on the Cr anode was bored by the common lithography technique.SiO₂ was etched with a mixed solution of fluorine and ammonium fluoride.It may be treated by dry etching.

The glass substrate was further coated with an organic layer and thinmetallic film by evaporation in a vacuum evaporation apparatus. Theorganic layer was composed of a hole-injecting layer of4,4′,4″-tris(3-methylphenylamino)triphenylamine (MTDATA),hole-transferring layer of bis(N-naphthyl)-N-phenylbenzidine (α-NPD) andlight-emitting layer of 8-quinolinol/aluminum complex (Alq). The thinmetallic film formed as the cathode on the organic layer was of amagnesium/silver alloy (Mg:Ag).

Each of the materials for the organic layer (0.2 g), and magnesium (0.1g) and silver (0.4 g) for the metallic layer, put in a boat forresistance heating, was set on a given electrode in a vacuum evaporationapparatus. A voltage was applied to each boat, after the vacuum chamberwas evacuated to 1.0×10⁻⁴ Pa, to heat them one by one. The glasssubstrate was masked with a metal during the evaporation process in sucha way that it was coated with the organic layer and metallic layer ofMg:Ag on given portions, i.e., the portions where chromium was exposedon the substrate. The evaporation mask was designed in such a way tocover the Cr-exposed portions totally and insulating layer edgespartially, because it is difficult to form the organic layer andmetallic film precisely by evaporation selectively on the Cr-exposedportions.

The glass substrate was first coated with a 30 nm thick MTDATA layer asthe hole-injecting layer, 20 nm thick α-NPD layer as thehole-transferring layer, and 50 nm thick Alq layer as the light-emittinglayer one by one in this order to form the organic layer. It was thencoated with a 10 nm thick metallic layer of Mg:Ag as the cathode on theorganic layer by co-evaporation of magnesium and silver. Magnesium wasmade into the film at a rate 9 times higher than silver.

The coated substrate was further coated with a transparent conductivethin film via the same mask in another vacuum chamber by DC sputtering.In this case, the In—W—Si—O-based, transparent conductive thin film,equivalent with that of EXAMPLE 23, was formed to a thickness of 200 nmunder the film-making conditions of sputtering gas: argon/oxygen mixture(Ar/O₂ ratio: 99/1 by volume), pressure: 0.6 Pa and DC power: 160 W. Thetransparent conductive thin film thus prepared showed goodelectroconductivity and transmission characteristics, although preparedat room temperature.

Finally, a 200 nm thick SiO₂ layer as a protective layer was provided bysputtering in such a way to totally cover the transparent,electroconductive film surface. This completed production of the organicEL device. It had a total of 16 image elements (8 by 2) placed atintervals of 2 mm, with 2 cathodes of equilibrium stripe type and 8anodes of equilibrium stripe type crossing each other to form the 16elements, 2 by 2 mm in size.

A DC voltage was applied to the organic EL device in an N₂ atmosphere tocontinuously drive it at a constant current density of 10 mA/cm², inorder to follow the average initial luminance, the number of currentleaks between the electrodes, the half life of light emission, andwhether dark spots were observed or not for 200 hours after lightemission was started for 160 image elements, which corresponded to theelements of 10 devices. The results are given in Table 10.

Example 77

An organic EL device with 16 image elements was prepared in the samemanner as in EXAMPLE 76, except that the transparent, electroconductivelayer for the cathode was replaced by the In—W—Si—O-based, thin,transparent, electroconductive layer, equivalent to that of EXAMPLE 25.The device was similarly analyzed for average initial luminance, numberof current leaks between the electrodes, half life of light emission,and whether dark spots were observed or not for 200 hours after lightemission was started for 160 image elements, which corresponded to theelements of 10 devices. The results are given in Table 10.

Example 78

An organic EL device with 16 image elements was prepared in the samemanner as in EXAMPLE 76, except that the transparent, electroconductivelayer for the cathode was replaced by the In—W—Si—O-based, thin,transparent, electroconductive layer, equivalent to that of EXAMPLE 34.The device was similarly analyzed for average initial luminance, numberof current leaks between the electrodes, half life of light emission,and whether dark spots were observed or not for 200 hours after lightemission was started for 160 image elements, which corresponded to theelements of 10 devices. The results are given in Table 10.

Example 79

An organic EL device with 16 image elements was prepared in the samemanner as in EXAMPLE 76, except that the transparent, electroconductivelayer for the cathode was replaced by the In—W—Si—O-based, thin,transparent, electroconductive layer, equivalent to that of EXAMPLE 38.The device was similarly analyzed for average initial luminance, numberof current leaks between the electrodes, half life of light emission,and whether dark spots were observed or not for 200 hours after lightemission was started for 160 image elements, which corresponded to theelements of 10 devices. The results are given in Table 10.

Comparative Example 20

An organic EL device with 16 image elements was prepared in the samemanner as in EXAMPLE 76, except that the transparent, electroconductivelayer for the cathode was replaced by the In—O-based, thin, transparent,electroconductive layer, equivalent to that of COMPARATIVE EXAMPLE 1.The device was similarly analyzed for average initial luminance, numberof current leaks between the electrodes, half life of light emission,and whether dark spots were observed or not for 200 hours after lightemission was started for 160 image elements, which corresponded to theelements of 10 devices. The results are given in Table 10.

Comparative Example 21

An organic EL device with 16 image elements was prepared in the samemanner as in EXAMPLE 76, except that the transparent, electroconductivelayer for the cathode was replaced by the In—Sn—O-based, thin,transparent, electroconductive layer, equivalent to that of COMPARATIVEEXAMPLE 3. The device was similarly analyzed for average initialluminance, number of current leaks between the electrodes, half life oflight emission, and whether dark spots (from which no light was emitted)were observed or not for 200 hours after light emission was started for160 image elements, which corresponded to the elements of 10 devices.The results are given in Table 10.

Comparative Example 22

An organic EL device with 16 image elements was prepared in the samemanner as in EXAMPLE 76, except that the transparent, electroconductivelayer for the cathode was replaced by an In—Zn—O-based, thin,transparent, electroconductive layer, which was prepared by DCsputtering with a sintered target of In₂O₃—ZnO (10% by weight) at afilm-making temperature of room temperature. The device was similarlyanalyzed for average initial luminance, number of current leaks betweenthe electrodes, half life of light emission, and whether dark spots(from which no light was emitted) were observed or not for 200 hoursafter light emission was started for 160 image elements, whichcorresponded to the elements of 10 devices. The results are given inTable 10.

TABLE 10 Average Half life of luminance luminance Dark spot EXAMPLE 76440 cd/m² 800 h Not observed 77 430 cd/m² 800 h Not observed 78 450cd/m² 800 h Not observed 79 480 cd/m² 800 h Not observed COMPARATIVEEXAMPLE 20 310 cd/m² 400 h A total of 35 spots observed per 10 mm square21 340 cd/m² 300 h A total of 21 spots observed per 10 mm square 22 350cd/m² 750 h Not observed

As shown in Table 10, each of the organic EL devices prepared inEXAMPLES 76 to 79 with the transparent conductive thin film of thepresent invention as the cathode had a higher average initial luminanceand apparently longer half life of luminance than any of the organic ELdevices prepared in COMPARATIVE EXAMPLES 20 to 22 using the conventionalmaterials. It was confirmed to have a luminance of 400 cd/m² or more,and a half life of luminance of 800 hours. A number of dark spots (fromwhich no light was emitted) were observed in each of the organic ELdevices prepared in COMPARATIVE EXAMPLES 20 to 22 using the conventionalmaterials for 200 hours after it started light emission. By contrast,each of the organic EL devices prepared in EXAMPLES 76 to 79 with thetransparent conductive thin film of the present invention as the cathodeshowed no dark spots in the same period. The organic EL device preparedin COMPARATIVE EXAMPLE 22 showed no dark spots (from which no light wasemitted) for 200 hours after it started light emission and a half lifeof luminance as long as those of the devices prepared in EXAMPLES 76 to79, but it showed a lower initial luminance.

It is clarified that the thin In—Zn—O film used as the cathode isinferior to the single, transparent conductive thin film of the presentinvention in light transmittance by the comparison test for lighttransmittance. This will account for lower luminance of the conventionaldevice. The XPS analysis of the thin In—Zn—O film clarified that itcontained metallic Zn, which is judged to be responsible for the lowertransmittance than that of the film of the present invention at around400 nm.

These organic EL devices prepared in the examples were tested for theirlight-emitting characteristics in a similar manner after they wereexposed to an atmosphere of 95% RH and 80° C. for 100 hours. It wasfound by these tests that the devices prepared in COMPARATIVE EXAMPLES21 and 22 showed a number of dark spots in the very initial stage oflight emission, whereas the organic EL devices prepared in EXAMPLES 76to 79 showed no dark spots even for 200 hours after light emission wasstarted, resulting from the high heat resistance of the transparentconductive thin film of the present invention.

Exactly the same tendency was observed with the devices that includedthe cathode of the In—W—Si—O-based amorphous thin film having thecomposition prepared in each of EXAMPLE 24, EXAMPLES 26 to 33, EXAMPLES35 to 37, and EXAMPLES 39 to 42 with the substrate kept at roomtemperature to 100° C. Therefore, these thin films of the presentinvention can make organic EL devices excellent in light-emittingcharacteristics, heat resistance and moisture resistance, and showing nodark spots.

An active matrix type organic EL device was prepared in a manner similarto that for EXAMPLE 76 using a glass substrate provided with a thin-filmtransistor and its circuit. It showed exactly the same results as theabove. Therefore, it can make an organic EL device excellent inlight-emitting characteristics, heat resistance and moisture resistance,and showing no dark spots.

Example 80

An organic EL device of the same structure was prepared in the samemanner as in EXAMPLE 76, except that the chromium anode, used for thoseprepared in EXAMPLES 76 to 79, was replaced by a palladium anode. Itshowed as excellent light-emitting characteristics as those prepared inEXAMPLES 76 to 79 using the Cr anode, and no dark spots even for 200hours after light emission was started.

Example 81

Organic EL devices of the same structure were prepared in the samemanner as in EXAMPLE 76, except that the cathode of the In—W—Si—O-based,amorphous, thin film, used for those prepared in EXAMPLES 76 to 79, wasreplaced by that of the In—Si—O-based, amorphous, thin film prepared inone of EXAMPLES 1 to 6 or that of the In—Sn—Si—O-based, amorphous, thinfilm prepared in one of EXAMPLES 7 to 22 with the substrate kept at roomtemperature to 300° C.

These organic EL devices showed as excellent light-emittingcharacteristics as those prepared in EXAMPLES 76 to 79 using the cathodeof the In—W—Si—O-based, amorphous, transparent conductive thin film, andno dark spots, even for 200 hours after light emission was started.

Example 82

Organic EL devices of the structure shown in FIG. 7 were prepared in thesame manner as in EXAMPLE 76, except that the metallic anode, used forthose prepared in EXAMPLES 76 to 79, was replaced by that of theIn—Si—O-based, In—Sn—Si—O-based or In—W—Si—O-based, amorphous, thin filmprepared in one of EXAMPLES 1 to 42 with the substrate kept at roomtemperature to 300° C.

These organic EL devices could emit light not only from the cathode butalso from the anode. Their light-emitting characteristics were analyzed.They showed as excellent light-emitting characteristics as thoseprepared in EXAMPLES, and no dark spots even for 200 hours after lightemission was started. However, the similar organic EL devices with theanode of In—Si—O-based or In—Sn—O-based thin film prepared in one ofCOMPARATIVE EXAMPLES 1 to 6 showed a number of dark spots for 200 hoursafter light emission was started.

Example 83

Organic EL devices of the structure shown in FIG. 7 were prepared on asubstrate of polyether sulfone (PES) film coated with a 1 μm thickacrylic-based hard coat layer (total thickness: 0.2 mm), which wasfurther coated with a 50 nm thick silicon oxynitride film.

They had an anode and cathode of the In—Si—O-based, In—Sn—Si—O-based orIn—W—Si—O-based, amorphous, transparent conductive thin film prepared inone of EXAMPLES 1 to 42 with the substrate kept at room temperature to120° C. They showed good light-emitting characteristics.

A transparent conductive thin film of silicon-doped indium oxide wasformed on a glass substrate by RF sputtering under the followingfilm-making conditions. The resulting thin film, although having aresistivity of 7.5×10⁻⁴ Ω·cm, was a transparent, crystalline,electroconductive film of very poor surface smoothness, having a numberof X-ray diffraction peaks and surface roughness Ra of 5.7 nm.

Film-making Conditions

Target composition: In₂O₃+SiO₂ (2% by weight), target size: 6 inches indiameter, gas pressure: 0.2 Pa, sputtering gas: pure Ar,target-substrate distance: 40 mm, RF power: 500 W, and the substrate notheated

An organic EL device of the structure shown in FIG. 7 was prepared inthe same manner as in EXAMPLE 76, except that the anode was replaced bythe one of the thin, In—Si—O-based film prepared in COMPARATIVE EXAMPLE23. It showed a number of dark spots for 200 hours after light emissionwere started.

Examples 84 to 87

The organic EL devices of the present invention were prepared by thefollowing procedure to have a laminate of thin In—W—Ge—O-based andMg—Ag-based films for the cathode, and chromium having a work functionof 4.5 eV for the anode. A 200 nm thick Cr film was formed on a glasssubstrate by DC sputtering with a Cr target having a diameter of 6inches under the conditions of sputtering gas: Ar, pressure: 0.4 Pa andDC power: 300 W. The Cr film was patterned by the common lithographytechnique, to have the anode of a given shape thereon.

Next, the glass substrate coated with the Cr anode was further coatedwith a 200 nm thick electrically insulating layer of silicon dioxide(SiO₂) by oxygen-reactive sputtering with a Si target. This insulatinglayer on the Cr anode was bored by the common lithography technique.SiO₂ was etched with a mixed solution of fluorine and ammonium fluoride.It may be treated by dry etching.

The glass substrate was further coated with an organic layer and thinmetallic film by evaporation in a vacuum evaporation apparatus. Theorganic layer was composed of a hole-injecting layer of4,4′,4″-tris(3-methylphenylamino)triphenylamine (MTDATA),hole-transferring layer of bis(N-naphthyl)-N-phenylbenzidine (α-NPD) andlight-emitting layer of 8-quinolinol/aluminum complex (Alq). The thinmetallic film formed as the cathode on the organic layer was of amagnesium/silver alloy (Mg:Ag).

Each of the materials for the organic layer (0.2 g), and magnesium (0.1g) and silver (0.4 g) for the metallic layer, put in a boat forresistance heating, was set on a given electrode in a vacuum evaporationapparatus. A voltage was applied to each boat, after the vacuum chamberwas evacuated to 1.0×10⁻⁴ Pa, to heat them one by one. The glasssubstrate was masked with a metal during the evaporation process in sucha way that it was coated with the organic layer and metallic layer ofMg:Ag on given portions, i.e., the portions where chromium was exposedon the substrate.

For evaporation of the organic layer and thin metallic layer, the glasssubstrate was first coated with a 30 nm thick MTDATA layer as thehole-injecting layer, 20 nm thick α-NPD layer as the hole-transferringlayer, and 50 nm thick Alq layer as the light-emitting layer one by onein this order to form the organic layer. It was then coated with a 10 nmthick thin metallic layer of Mg:Ag as the cathode on the organic layerby co-evaporation of magnesium and silver. Magnesium was made into thefilm at a rate 9 times higher than silver.

The coated substrate was further coated with a 200 nm thick, transparentconductive thin film via the same mask by DC sputtering in anothervacuum chamber, into which the whole coated substrate was transferred,to form the cathode composed of this film and the thin metallic film.The conditions for making the electroconductive film were sputteringgas: argon/oxygen mixture (Ar/O₂ ratio:99/1 by volume), pressure:0.6 Paand DC power: 160 W.

Finally, a 200 nm thick SiO₂ layer as a protective layer was provided bysputtering in such a way to totally cover the transparent,electroconductive film surface. This completed production of the organicEL device. The organic EL devices prepared in EXAMPLES 84 to 87 used atransparent conductive thin film having the composition prepared inEXAMPLES 47, 51, 46 and 43, respectively. Each device had a total of 16image elements (8 by 2) placed at intervals of 2 mm, with 2 cathodes ofequilibrium stripe type and 8 anodes of equilibrium stripe type crossingeach other to form the 16 elements, 2 by 2 mm in size.

Comparative Examples 25 to 27

An organic EL device of the same structure was prepared in each of thesecomparative examples in the same manner as in EXAMPLES 84 to 87, exceptthat the transparent conductive thin film was replaced by the thin filmprepared in COMPARATIVE EXAMPLES 7 and 9 for COMPARATIVE EXAMPLES 25 and26, respectively, and by an In₂O₃—ZnO-based, transparent conductive thinfilm (equivalent with that prepared in COMPARATIVE EXAMPLE 22) forCOMPARATIVE EXAMPLE 27, where the In₂O₃—ZnO-based film was prepared byDC sputtering with a sintered target of In₂O₃ doped with 10% by weightof ZnO and a substrate kept at room temperature.

A DC voltage was applied to each organic EL device in an N₂ atmosphereto continuously drive it at a constant current density of 10 mA/cm², inorder to follow average initial luminance, half life of light emission,and whether dark spots were observed or not for 200 hours after lightemission was started for 160 image elements, which corresponded to theelements of 10 devices. The results are given in Table 11.

TABLE 11 Average Half life of luminance luminance (cd/m²) (hour) Darkspot EXAMPLE 84 450 800 Not observed 85 420 800 Not observed 86 400 800Not observed 87 410 800 Not observed COMPARATIVE EXAMPLE 25 300 600 Atotal of 9 spots observed per 10 mm square 26 320 300 A total of 23spots observed per 10 mm square 27 350 800 Not observed

As shown in Table 11, each of the organic EL devices prepared inEXAMPLES 84 to 87 with the transparent conductive thin film of thepresent invention as the cathode was confirmed to have a higher averageinitial luminance of 400 cd/m² or more and an apparently longer halflife of luminance of 800 hours more than any of the organic EL devicesprepared in COMPARATIVE EXAMPLES 25 to 27 using the conventionalmaterials. A number of dark spots (from which no light was emitted) wereobserved in each of the organic. EL devices prepared in COMPARATIVEEXAMPLES 25 to 27 for 200 hours after it started light emission. Bycontrast, each of the organic EL devices prepared in EXAMPLES 84 to 87showed no dark spots in the same period.

The organic EL device prepared in COMPARATIVE EXAMPLE 27, which used andIn₂O₃—ZnO-based, transparent conductive thin film, showed no dark spots(from which no light was emitted) for 200 hours after it started lightemission and a half life of luminance of 800 hours, which was as long asthat of the devices of the present invention. However, its initialluminance is only 350 cd/m², much lower than that of the devices of thepresent invention. The lower luminance conceivably resulted frominsufficient light transmittance of the thin, In₂O₃—ZnO-based film usedfor the cathode. The XPS analysis of the thin, In₂O₃—ZnO-based filmclarified that it contained metallic Zn, which is judged to beresponsible for the much lower transmittance than that of the film ofthe present invention at around 400 nm.

The organic EL devices prepared in these examples were tested for theirlight-emitting characteristics in a similar manner after they wereexposed to an atmosphere of 95% RH and 80° C. for 100 hours. It wasfound by these tests that the devices prepared in COMPARATIVE EXAMPLES25 to 27 showed a number of dark spots in the very initial stage oflight emission, whereas those prepared in EXAMPLES 84 to 87 showed nodark spots even for 200 hours after light emission was started. Thismeans that the transparent conductive thin films of the presentinvention are also excellent in heat resistance.

An organic EL device of the same structure was prepared in the samemanner as in EXAMPLES 84 to 87, except that the substrate was replacedby a glass substrate provided with a thin-film transistor and itscircuit. It showed excellent light-emitting characteristics, like thoseprepared in EXAMPLES 84 to 87. It showed no dark spots even for 200hours after light emission was started.

Examples 88 to 91

Organic EL devices of the same structure were prepared in the samemanner as in EXAMPLES 84 to 87, except that the chromium (Cr) anode wasreplaced by a palladium (Pd) anode and the cathode of thin Mg—Ag alloyfilm was replaced by a cathode composed only of the transparentconductive thin film of the present invention. These organic EL deviceswith the Pd anode showed as excellent light-emitting characteristics asthose with the Cr anode, prepared in EXAMPLES 84 to 87 with the Cranode, and no dark spots even for 200 hours after light emission wasstarted.

Organic EL devices of the same structure were also prepared in the samemanner as in EXAMPLES 84 to 87, except that the anode of Cr was replacedby that of a transparent conductive thin film having the compositionequivalent with that prepared in one of EXAMPLES 52 to 70. These organicEL devices could emit light not only from the cathode but also from theanode. Their light-emitting characteristics were analyzed. They showedas excellent light-emitting characteristics as those prepared inEXAMPLES 84 to 87, and no dark spots even for 200 hours after lightemission was started. However, the similar organic EL devices with theanode of In₂O₃—Ge-based or In₂O₃—Sn (ITO)-based thin film prepared inone of COMPARATIVE EXAMPLES 7 to 14 showed a number of dark spots for200 hours after light emission was started.

Organic EL devices of the same structure were prepared, in a mannersimilar to those for EXAMPLES 84 to 87, on a substrate of polyethersulfone (PES) film coated with 1 μm thick acrylic-based hard coat layer(total thickness: 0.2 mm), which was further coated with a 50 nm thicksilicon oxynitride film. They had an anode and cathode of a transparentconductive thin film having the composition equivalent with thatprepared in one of EXAMPLES 43 to 51. They showed good light-emittingcharacteristics.

Advantages of the Invention

As described above in detail, the transparent conductive thin film ofthe present invention is very excellent in surface smoothness, becauseit is completely free of any crystalline phase and completely amorphous,and low in resistance and at least as excellent as an indium tin oxide(ITO) film in transmittance of visible rays including the low-wavelengthregion. This thin film can be easily formed on a substrate by the commonsputtering or ion plating method in the presence of the sintered targetof the present invention.

Moreover, the transparent conductive thin film and substrate on whichthe film is formed are very useful for transparent electrodes not onlyfor organic EL devices, which need a transparent electrode of smoothsurface and low electrical resistance, but also for inorganic EL devicesand display devices, e.g., LCDs. Therefore, the transparent conductivethin film of the present invention is of very high industrial value,because it can give an organic EL device high in luminance, long in halflife of luminance, causing no dark spots and high in durability.

1. A sintered target for producing the transparent conductive thin filmcontaining indium oxide as the major component and silicon, having asubstantially amorphous structure, wherein the sintered target comprisessintered indium oxide doped with silicon and tungsten.
 2. A process forproducing a thin, amorphous, transparent, electroconductive filmcomprising silicon-doped indium oxide on a substrate, said processcomprising sputtering a substrate in an oxygen-containing inert gasatmosphere in a sputtering apparatus which contains the substrate andsintered target of one of selected from the group consisting of sinteredindium oxide doped with silicon and indium oxide doped with silicontogether with tin and/or tungsten.
 3. The process according to claim 2for producing a thin, amorphous, transparent, electroconductive film,wherein said substrate is heated at 100 to 300° C.
 4. The processaccording to claim 2 for producing a thin, amorphous, transparent,electroconductive film, wherein said inert gas is a mixture of argon andoxygen containing oxygen at 1% or more.
 5. The process according toclaim 2 for producing a thin, amorphous, transparent, electroconductivefilm, wherein said film is produced by DC sputtering in anoxygen-containing inert gas atmosphere after pressure in the sputteringapparatus is set at 0.1 to 1 Pa.